<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with Wdesk from Workiva-->
<!--Copyright 2021 Workiva-->
<!--r:8c5cbfda-8bc1-429d-b97d-a8d1aa97dc81,g:a0195183-61e0-415b-a153-bfed4a12853e-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://www.datadoghq.com/role/CoverPage" xlink:type="simple" xlink:href="ddog-20210630.xsd#CoverPage"/>
  <link:definitionLink xlink:role="http://www.datadoghq.com/role/CoverPage" xlink:type="extended" id="i5c06a97c3561418ba1ed6e26bb17926e_CoverPage">
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationLineItems_fd269072-15b4-4b48-ba96-9e5f53394903" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_DocumentInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentType_7215971e-9baa-4def-92aa-8a7007790e95" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_DocumentType"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_fd269072-15b4-4b48-ba96-9e5f53394903" xlink:to="loc_dei_DocumentType_7215971e-9baa-4def-92aa-8a7007790e95" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentQuarterlyReport_6cfc2b1a-bd6b-483d-838b-bf86457d3a3d" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_DocumentQuarterlyReport"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_fd269072-15b4-4b48-ba96-9e5f53394903" xlink:to="loc_dei_DocumentQuarterlyReport_6cfc2b1a-bd6b-483d-838b-bf86457d3a3d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentPeriodEndDate_f55d2fcc-af17-4cfb-bcd7-75f75227d1ed" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_DocumentPeriodEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_fd269072-15b4-4b48-ba96-9e5f53394903" xlink:to="loc_dei_DocumentPeriodEndDate_f55d2fcc-af17-4cfb-bcd7-75f75227d1ed" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentTransitionReport_bc2e4cc4-f6a9-46f5-bb0c-442ed59fed6a" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_DocumentTransitionReport"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_fd269072-15b4-4b48-ba96-9e5f53394903" xlink:to="loc_dei_DocumentTransitionReport_bc2e4cc4-f6a9-46f5-bb0c-442ed59fed6a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFileNumber_9b708933-498b-4cec-914d-c762083232a2" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_EntityFileNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_fd269072-15b4-4b48-ba96-9e5f53394903" xlink:to="loc_dei_EntityFileNumber_9b708933-498b-4cec-914d-c762083232a2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityRegistrantName_89afd0e7-59cc-4b6b-9d8b-ab6eab7bec28" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_EntityRegistrantName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_fd269072-15b4-4b48-ba96-9e5f53394903" xlink:to="loc_dei_EntityRegistrantName_89afd0e7-59cc-4b6b-9d8b-ab6eab7bec28" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityIncorporationStateCountryCode_2e0611ed-91ff-45d4-b1aa-86ff2b630288" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_EntityIncorporationStateCountryCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_fd269072-15b4-4b48-ba96-9e5f53394903" xlink:to="loc_dei_EntityIncorporationStateCountryCode_2e0611ed-91ff-45d4-b1aa-86ff2b630288" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityTaxIdentificationNumber_402031c3-f310-4e7d-b3cc-264e953a3401" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_EntityTaxIdentificationNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_fd269072-15b4-4b48-ba96-9e5f53394903" xlink:to="loc_dei_EntityTaxIdentificationNumber_402031c3-f310-4e7d-b3cc-264e953a3401" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine1_f08d3651-6d69-4dae-90a1-ce64b5d00928" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_EntityAddressAddressLine1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_fd269072-15b4-4b48-ba96-9e5f53394903" xlink:to="loc_dei_EntityAddressAddressLine1_f08d3651-6d69-4dae-90a1-ce64b5d00928" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine2_f1c8ebc3-1896-4d6c-b878-2971683e5506" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_EntityAddressAddressLine2"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_fd269072-15b4-4b48-ba96-9e5f53394903" xlink:to="loc_dei_EntityAddressAddressLine2_f1c8ebc3-1896-4d6c-b878-2971683e5506" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressCityOrTown_a4e1c594-9c50-430a-a45d-40ca3a0b8444" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_EntityAddressCityOrTown"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_fd269072-15b4-4b48-ba96-9e5f53394903" xlink:to="loc_dei_EntityAddressCityOrTown_a4e1c594-9c50-430a-a45d-40ca3a0b8444" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressStateOrProvince_b90d4c22-f704-4e60-ba9c-0ed8a66e5093" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_EntityAddressStateOrProvince"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_fd269072-15b4-4b48-ba96-9e5f53394903" xlink:to="loc_dei_EntityAddressStateOrProvince_b90d4c22-f704-4e60-ba9c-0ed8a66e5093" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressPostalZipCode_e06602ca-22a2-4f8f-a590-1ffe3565e772" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_EntityAddressPostalZipCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_fd269072-15b4-4b48-ba96-9e5f53394903" xlink:to="loc_dei_EntityAddressPostalZipCode_e06602ca-22a2-4f8f-a590-1ffe3565e772" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CityAreaCode_28c8b5f5-fb69-455e-8254-d44b4e3a9b69" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_CityAreaCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_fd269072-15b4-4b48-ba96-9e5f53394903" xlink:to="loc_dei_CityAreaCode_28c8b5f5-fb69-455e-8254-d44b4e3a9b69" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LocalPhoneNumber_970d418c-25d6-4ba6-ba88-b86e6f062ac3" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_LocalPhoneNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_fd269072-15b4-4b48-ba96-9e5f53394903" xlink:to="loc_dei_LocalPhoneNumber_970d418c-25d6-4ba6-ba88-b86e6f062ac3" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_Security12bTitle_74258224-e378-42ae-8a9f-5860e54428eb" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_Security12bTitle"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_fd269072-15b4-4b48-ba96-9e5f53394903" xlink:to="loc_dei_Security12bTitle_74258224-e378-42ae-8a9f-5860e54428eb" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_TradingSymbol_29f05722-15c0-4f5f-a842-24b583a01ec2" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_TradingSymbol"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_fd269072-15b4-4b48-ba96-9e5f53394903" xlink:to="loc_dei_TradingSymbol_29f05722-15c0-4f5f-a842-24b583a01ec2" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SecurityExchangeName_73c180f1-bd62-4f26-a476-2e7c042b05b4" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_SecurityExchangeName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_fd269072-15b4-4b48-ba96-9e5f53394903" xlink:to="loc_dei_SecurityExchangeName_73c180f1-bd62-4f26-a476-2e7c042b05b4" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCurrentReportingStatus_6e1ee48d-681d-43c1-8816-9e8e90fd78d3" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_EntityCurrentReportingStatus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_fd269072-15b4-4b48-ba96-9e5f53394903" xlink:to="loc_dei_EntityCurrentReportingStatus_6e1ee48d-681d-43c1-8816-9e8e90fd78d3" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityInteractiveDataCurrent_6351b631-99b4-49c9-964a-6ec1ae93b21d" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_EntityInteractiveDataCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_fd269072-15b4-4b48-ba96-9e5f53394903" xlink:to="loc_dei_EntityInteractiveDataCurrent_6351b631-99b4-49c9-964a-6ec1ae93b21d" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFilerCategory_ca2a9d65-7f4b-4eb2-8ef9-09887c31d6b7" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_EntityFilerCategory"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_fd269072-15b4-4b48-ba96-9e5f53394903" xlink:to="loc_dei_EntityFilerCategory_ca2a9d65-7f4b-4eb2-8ef9-09887c31d6b7" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitySmallBusiness_59c6c225-4ff4-4590-955e-4d8663b99627" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_EntitySmallBusiness"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_fd269072-15b4-4b48-ba96-9e5f53394903" xlink:to="loc_dei_EntitySmallBusiness_59c6c225-4ff4-4590-955e-4d8663b99627" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityEmergingGrowthCompany_ce6f37b4-d90c-4768-87d1-e5e9109b0e91" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_EntityEmergingGrowthCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_fd269072-15b4-4b48-ba96-9e5f53394903" xlink:to="loc_dei_EntityEmergingGrowthCompany_ce6f37b4-d90c-4768-87d1-e5e9109b0e91" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityShellCompany_797b801c-4d42-4114-903b-95f86e422672" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_EntityShellCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_fd269072-15b4-4b48-ba96-9e5f53394903" xlink:to="loc_dei_EntityShellCompany_797b801c-4d42-4114-903b-95f86e422672" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCommonStockSharesOutstanding_3449d9c9-b544-42f7-8738-c4a88a1ef147" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_EntityCommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_fd269072-15b4-4b48-ba96-9e5f53394903" xlink:to="loc_dei_EntityCommonStockSharesOutstanding_3449d9c9-b544-42f7-8738-c4a88a1ef147" xlink:type="arc" order="24"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AmendmentFlag_a5d5eadc-30f6-4911-aee2-9b28bb2ad6cd" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_AmendmentFlag"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_fd269072-15b4-4b48-ba96-9e5f53394903" xlink:to="loc_dei_AmendmentFlag_a5d5eadc-30f6-4911-aee2-9b28bb2ad6cd" xlink:type="arc" order="25"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalYearFocus_d5be241f-cc8a-420f-9bd3-50fb03c79870" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_DocumentFiscalYearFocus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_fd269072-15b4-4b48-ba96-9e5f53394903" xlink:to="loc_dei_DocumentFiscalYearFocus_d5be241f-cc8a-420f-9bd3-50fb03c79870" xlink:type="arc" order="26"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalPeriodFocus_e93a0752-f5f2-44d6-b64a-5580fbb787ed" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_DocumentFiscalPeriodFocus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_fd269072-15b4-4b48-ba96-9e5f53394903" xlink:to="loc_dei_DocumentFiscalPeriodFocus_e93a0752-f5f2-44d6-b64a-5580fbb787ed" xlink:type="arc" order="27"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCentralIndexKey_cabff488-6af0-4687-8403-76674156db51" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_EntityCentralIndexKey"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_fd269072-15b4-4b48-ba96-9e5f53394903" xlink:to="loc_dei_EntityCentralIndexKey_cabff488-6af0-4687-8403-76674156db51" xlink:type="arc" order="28"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CurrentFiscalYearEndDate_ed7e67ab-f83e-48e7-b848-3702125dec34" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_CurrentFiscalYearEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_fd269072-15b4-4b48-ba96-9e5f53394903" xlink:to="loc_dei_CurrentFiscalYearEndDate_ed7e67ab-f83e-48e7-b848-3702125dec34" xlink:type="arc" order="29"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationTable_248f5956-44d5-4de3-82ab-8d3484e4a3fb" xlink:href="https://xbrl.sec.gov/dei/2021/dei-2021.xsd#dei_DocumentInformationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dei_DocumentInformationLineItems_fd269072-15b4-4b48-ba96-9e5f53394903" xlink:to="loc_dei_DocumentInformationTable_248f5956-44d5-4de3-82ab-8d3484e4a3fb" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_d8d6a59d-e05d-44f8-a485-51c6d05abbcb" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_DocumentInformationTable_248f5956-44d5-4de3-82ab-8d3484e4a3fb" xlink:to="loc_us-gaap_StatementClassOfStockAxis_d8d6a59d-e05d-44f8-a485-51c6d05abbcb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_d8d6a59d-e05d-44f8-a485-51c6d05abbcb_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_d8d6a59d-e05d-44f8-a485-51c6d05abbcb" xlink:to="loc_us-gaap_ClassOfStockDomain_d8d6a59d-e05d-44f8-a485-51c6d05abbcb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_a011be17-0b0f-4af9-942f-e0545e29f3d2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_d8d6a59d-e05d-44f8-a485-51c6d05abbcb" xlink:to="loc_us-gaap_ClassOfStockDomain_a011be17-0b0f-4af9-942f-e0545e29f3d2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_78f59ae4-5f74-4dee-9cda-98d336f2a410" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_a011be17-0b0f-4af9-942f-e0545e29f3d2" xlink:to="loc_us-gaap_CommonClassAMember_78f59ae4-5f74-4dee-9cda-98d336f2a410" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_6d8fb6b3-2c79-4650-86b9-189cb2fb7694" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_a011be17-0b0f-4af9-942f-e0545e29f3d2" xlink:to="loc_us-gaap_CommonClassBMember_6d8fb6b3-2c79-4650-86b9-189cb2fb7694" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.datadoghq.com/role/CONDENSEDCONSOLIDATEDBALANCESHEETS" xlink:type="simple" xlink:href="ddog-20210630.xsd#CONDENSEDCONSOLIDATEDBALANCESHEETS"/>
  <link:definitionLink xlink:role="http://www.datadoghq.com/role/CONDENSEDCONSOLIDATEDBALANCESHEETS" xlink:type="extended" id="if46412f72e2d4a22984ab478220e66dc_CONDENSEDCONSOLIDATEDBALANCESHEETS">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_5a3dbd8f-56a5-4aee-80f5-c6f6c1d279e0" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsAbstract_270af3e7-41ac-4c96-b632-ceb8fc53504b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AssetsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_5a3dbd8f-56a5-4aee-80f5-c6f6c1d279e0" xlink:to="loc_us-gaap_AssetsAbstract_270af3e7-41ac-4c96-b632-ceb8fc53504b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrentAbstract_d1fee4c6-fe48-4ffd-98c0-0f80cfcd33d3" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AssetsCurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_270af3e7-41ac-4c96-b632-ceb8fc53504b" xlink:to="loc_us-gaap_AssetsCurrentAbstract_d1fee4c6-fe48-4ffd-98c0-0f80cfcd33d3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_8fa054f4-ebb8-482a-9290-16418e93c2fa" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_d1fee4c6-fe48-4ffd-98c0-0f80cfcd33d3" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_8fa054f4-ebb8-482a-9290-16418e93c2fa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecuritiesCurrent_fcf908f9-0ad4-4d95-b2da-47f9bf5e9c73" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecuritiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_d1fee4c6-fe48-4ffd-98c0-0f80cfcd33d3" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecuritiesCurrent_fcf908f9-0ad4-4d95-b2da-47f9bf5e9c73" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableNetCurrent_d24a491a-f09a-47d2-9d56-8c0ee5ca1d78" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AccountsReceivableNetCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_d1fee4c6-fe48-4ffd-98c0-0f80cfcd33d3" xlink:to="loc_us-gaap_AccountsReceivableNetCurrent_d24a491a-f09a-47d2-9d56-8c0ee5ca1d78" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredCostsCurrent_008062d4-efb1-4515-8ccf-463ca5cb83fd" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DeferredCostsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_d1fee4c6-fe48-4ffd-98c0-0f80cfcd33d3" xlink:to="loc_us-gaap_DeferredCostsCurrent_008062d4-efb1-4515-8ccf-463ca5cb83fd" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_51a7f0b0-5f2c-4df8-9978-51db58c7f3e4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PrepaidExpenseAndOtherAssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_d1fee4c6-fe48-4ffd-98c0-0f80cfcd33d3" xlink:to="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_51a7f0b0-5f2c-4df8-9978-51db58c7f3e4" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrent_8715ca50-8536-4451-856e-2da7f4a4aafb" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_d1fee4c6-fe48-4ffd-98c0-0f80cfcd33d3" xlink:to="loc_us-gaap_AssetsCurrent_8715ca50-8536-4451-856e-2da7f4a4aafb" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_d0b5218e-b75c-43ae-8e02-0f3880251012" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_270af3e7-41ac-4c96-b632-ceb8fc53504b" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_d0b5218e-b75c-43ae-8e02-0f3880251012" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseRightOfUseAsset_5569f7f9-e172-475c-8ef1-d07795b791fb" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OperatingLeaseRightOfUseAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_270af3e7-41ac-4c96-b632-ceb8fc53504b" xlink:to="loc_us-gaap_OperatingLeaseRightOfUseAsset_5569f7f9-e172-475c-8ef1-d07795b791fb" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_ab3b4967-327e-4aea-b731-ccf1195dd4c2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_270af3e7-41ac-4c96-b632-ceb8fc53504b" xlink:to="loc_us-gaap_Goodwill_ab3b4967-327e-4aea-b731-ccf1195dd4c2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_c4cac81c-d3f1-4206-90b2-7ba0f861c5da" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_270af3e7-41ac-4c96-b632-ceb8fc53504b" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_c4cac81c-d3f1-4206-90b2-7ba0f861c5da" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredCosts_c66427b4-2d59-43ed-8e07-3e4db6d04839" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DeferredCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_270af3e7-41ac-4c96-b632-ceb8fc53504b" xlink:to="loc_us-gaap_DeferredCosts_c66427b4-2d59-43ed-8e07-3e4db6d04839" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashNoncurrent_e452d9a4-9ff5-45d5-b4ff-201ba91399a2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RestrictedCashNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_270af3e7-41ac-4c96-b632-ceb8fc53504b" xlink:to="loc_us-gaap_RestrictedCashNoncurrent_e452d9a4-9ff5-45d5-b4ff-201ba91399a2" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsNoncurrent_21d567a5-9035-4b9f-b371-7b5567075c3d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OtherAssetsNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_270af3e7-41ac-4c96-b632-ceb8fc53504b" xlink:to="loc_us-gaap_OtherAssetsNoncurrent_21d567a5-9035-4b9f-b371-7b5567075c3d" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_86e10853-b823-4400-a0de-ad13c518063c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_270af3e7-41ac-4c96-b632-ceb8fc53504b" xlink:to="loc_us-gaap_Assets_86e10853-b823-4400-a0de-ad13c518063c" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_2b0812ea-8184-4612-bb46-7768026c079c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LiabilitiesAndStockholdersEquityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_5a3dbd8f-56a5-4aee-80f5-c6f6c1d279e0" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_2b0812ea-8184-4612-bb46-7768026c079c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrentAbstract_440fd5d5-9762-4d20-b226-b2fbec295c7f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LiabilitiesCurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_2b0812ea-8184-4612-bb46-7768026c079c" xlink:to="loc_us-gaap_LiabilitiesCurrentAbstract_440fd5d5-9762-4d20-b226-b2fbec295c7f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableCurrent_7c5a5696-0a12-4c2a-b960-fe14a131cfbf" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AccountsPayableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_440fd5d5-9762-4d20-b226-b2fbec295c7f" xlink:to="loc_us-gaap_AccountsPayableCurrent_7c5a5696-0a12-4c2a-b960-fe14a131cfbf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedLiabilitiesAndOtherLiabilities_27baba83-7fa4-4483-80c7-d889e05e522b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AccruedLiabilitiesAndOtherLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_440fd5d5-9762-4d20-b226-b2fbec295c7f" xlink:to="loc_us-gaap_AccruedLiabilitiesAndOtherLiabilities_27baba83-7fa4-4483-80c7-d889e05e522b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLiabilityCurrent_ef9e3239-cc73-43b5-9343-a518a0133eba" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OperatingLeaseLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_440fd5d5-9762-4d20-b226-b2fbec295c7f" xlink:to="loc_us-gaap_OperatingLeaseLiabilityCurrent_ef9e3239-cc73-43b5-9343-a518a0133eba" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityCurrent_98db26ca-5780-41d4-81e9-4dfd6ac15863" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ContractWithCustomerLiabilityCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_440fd5d5-9762-4d20-b226-b2fbec295c7f" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityCurrent_98db26ca-5780-41d4-81e9-4dfd6ac15863" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrent_75b99704-628c-4101-9da5-eb7a85ceb7d5" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_440fd5d5-9762-4d20-b226-b2fbec295c7f" xlink:to="loc_us-gaap_LiabilitiesCurrent_75b99704-628c-4101-9da5-eb7a85ceb7d5" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLiabilityNoncurrent_07bcedb3-f1a0-4f31-a4b4-eb1d07a0dce8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OperatingLeaseLiabilityNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_2b0812ea-8184-4612-bb46-7768026c079c" xlink:to="loc_us-gaap_OperatingLeaseLiabilityNoncurrent_07bcedb3-f1a0-4f31-a4b4-eb1d07a0dce8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleLongTermNotesPayable_a84952a1-c689-4603-9bdd-0a767cc0f313" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConvertibleLongTermNotesPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_2b0812ea-8184-4612-bb46-7768026c079c" xlink:to="loc_us-gaap_ConvertibleLongTermNotesPayable_a84952a1-c689-4603-9bdd-0a767cc0f313" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityNoncurrent_48f2c645-3fef-4c7e-9385-920c36cbcec1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ContractWithCustomerLiabilityNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_2b0812ea-8184-4612-bb46-7768026c079c" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityNoncurrent_48f2c645-3fef-4c7e-9385-920c36cbcec1" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilitiesNoncurrent_0940ac48-f10d-432b-9aba-45c7e11c646a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OtherLiabilitiesNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_2b0812ea-8184-4612-bb46-7768026c079c" xlink:to="loc_us-gaap_OtherLiabilitiesNoncurrent_0940ac48-f10d-432b-9aba-45c7e11c646a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Liabilities_baa6af2e-220b-4f9c-a28e-d4e6db533ce3" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_Liabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_2b0812ea-8184-4612-bb46-7768026c079c" xlink:to="loc_us-gaap_Liabilities_baa6af2e-220b-4f9c-a28e-d4e6db533ce3" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommitmentsAndContingencies_3b9514f5-3a44-464c-96a8-38c5c50e68d4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommitmentsAndContingencies"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_2b0812ea-8184-4612-bb46-7768026c079c" xlink:to="loc_us-gaap_CommitmentsAndContingencies_3b9514f5-3a44-464c-96a8-38c5c50e68d4" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityAbstract_9678fe42-22e4-4985-a8ad-a28173acbc9c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockholdersEquityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_2b0812ea-8184-4612-bb46-7768026c079c" xlink:to="loc_us-gaap_StockholdersEquityAbstract_9678fe42-22e4-4985-a8ad-a28173acbc9c" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockValue_faef32e0-3293-4842-bb70-59c21b23f9c6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_9678fe42-22e4-4985-a8ad-a28173acbc9c" xlink:to="loc_us-gaap_CommonStockValue_faef32e0-3293-4842-bb70-59c21b23f9c6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalCommonStock_cc75996b-3db3-4eec-a729-cc87dd347af7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AdditionalPaidInCapitalCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_9678fe42-22e4-4985-a8ad-a28173acbc9c" xlink:to="loc_us-gaap_AdditionalPaidInCapitalCommonStock_cc75996b-3db3-4eec-a729-cc87dd347af7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_2984a3e0-9637-480e-9756-eafce69fa671" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_9678fe42-22e4-4985-a8ad-a28173acbc9c" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_2984a3e0-9637-480e-9756-eafce69fa671" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsAccumulatedDeficit_b52993d1-ef0f-4f68-b93f-23af1c0575bc" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RetainedEarningsAccumulatedDeficit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_9678fe42-22e4-4985-a8ad-a28173acbc9c" xlink:to="loc_us-gaap_RetainedEarningsAccumulatedDeficit_b52993d1-ef0f-4f68-b93f-23af1c0575bc" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_3d400842-31a1-4df9-afe1-546f8d612388" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_9678fe42-22e4-4985-a8ad-a28173acbc9c" xlink:to="loc_us-gaap_StockholdersEquity_3d400842-31a1-4df9-afe1-546f8d612388" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquity_b8d1be17-12e5-460c-84da-13255e47e20f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LiabilitiesAndStockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_2b0812ea-8184-4612-bb46-7768026c079c" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquity_b8d1be17-12e5-460c-84da-13255e47e20f" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_ea9e25e0-1e45-4dfa-b00b-947fd794dcd6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_5a3dbd8f-56a5-4aee-80f5-c6f6c1d279e0" xlink:to="loc_us-gaap_StatementTable_ea9e25e0-1e45-4dfa-b00b-947fd794dcd6" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_893902f9-ea2f-4de1-8fa9-4ad13894e509" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_ea9e25e0-1e45-4dfa-b00b-947fd794dcd6" xlink:to="loc_us-gaap_StatementClassOfStockAxis_893902f9-ea2f-4de1-8fa9-4ad13894e509" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_893902f9-ea2f-4de1-8fa9-4ad13894e509_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_893902f9-ea2f-4de1-8fa9-4ad13894e509" xlink:to="loc_us-gaap_ClassOfStockDomain_893902f9-ea2f-4de1-8fa9-4ad13894e509_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_ace467dd-34f0-4d70-9cbe-258681a9352e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_893902f9-ea2f-4de1-8fa9-4ad13894e509" xlink:to="loc_us-gaap_ClassOfStockDomain_ace467dd-34f0-4d70-9cbe-258681a9352e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_93f6546a-0c7b-43c2-b941-bbe9749fac86" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_ace467dd-34f0-4d70-9cbe-258681a9352e" xlink:to="loc_us-gaap_CommonClassAMember_93f6546a-0c7b-43c2-b941-bbe9749fac86" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_1cdb421a-33db-4227-a7ef-ba0908174d49" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_ace467dd-34f0-4d70-9cbe-258681a9352e" xlink:to="loc_us-gaap_CommonClassBMember_1cdb421a-33db-4227-a7ef-ba0908174d49" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.datadoghq.com/role/CONDENSEDCONSOLIDATEDBALANCESHEETSParenthetical" xlink:type="simple" xlink:href="ddog-20210630.xsd#CONDENSEDCONSOLIDATEDBALANCESHEETSParenthetical"/>
  <link:definitionLink xlink:role="http://www.datadoghq.com/role/CONDENSEDCONSOLIDATEDBALANCESHEETSParenthetical" xlink:type="extended" id="ic1b15a6497d04325a9993de4fc32aa53_CONDENSEDCONSOLIDATEDBALANCESHEETSParenthetical">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_fef9d3e4-3a09-4fc6-95d0-290f0d742f86" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_7362ad28-c441-45a6-8344-8cfd0990fd27" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_fef9d3e4-3a09-4fc6-95d0-290f0d742f86" xlink:to="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_7362ad28-c441-45a6-8344-8cfd0990fd27" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_a8419fc9-c1ab-48cf-801a-c608d536f9a9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_fef9d3e4-3a09-4fc6-95d0-290f0d742f86" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_a8419fc9-c1ab-48cf-801a-c608d536f9a9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_6327a960-723b-457a-81c9-df413892dadd" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_fef9d3e4-3a09-4fc6-95d0-290f0d742f86" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_6327a960-723b-457a-81c9-df413892dadd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_3fc37488-e37c-4555-8be7-5711f322c158" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_fef9d3e4-3a09-4fc6-95d0-290f0d742f86" xlink:to="loc_us-gaap_CommonStockSharesIssued_3fc37488-e37c-4555-8be7-5711f322c158" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_21c1a5bc-8aa2-4b20-873e-a88eaf13f1c7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_fef9d3e4-3a09-4fc6-95d0-290f0d742f86" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_21c1a5bc-8aa2-4b20-873e-a88eaf13f1c7" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_cef70782-659f-4131-a706-306969578a76" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_fef9d3e4-3a09-4fc6-95d0-290f0d742f86" xlink:to="loc_us-gaap_StatementTable_cef70782-659f-4131-a706-306969578a76" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_e3639245-4124-4cc6-a86c-d757740f60c1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_cef70782-659f-4131-a706-306969578a76" xlink:to="loc_us-gaap_StatementClassOfStockAxis_e3639245-4124-4cc6-a86c-d757740f60c1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_e3639245-4124-4cc6-a86c-d757740f60c1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_e3639245-4124-4cc6-a86c-d757740f60c1" xlink:to="loc_us-gaap_ClassOfStockDomain_e3639245-4124-4cc6-a86c-d757740f60c1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_9dc09689-e9b3-47f7-b654-0abe0fda937b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_e3639245-4124-4cc6-a86c-d757740f60c1" xlink:to="loc_us-gaap_ClassOfStockDomain_9dc09689-e9b3-47f7-b654-0abe0fda937b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_82c7229d-b606-430f-9514-6ccb6b2388c1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_9dc09689-e9b3-47f7-b654-0abe0fda937b" xlink:to="loc_us-gaap_CommonClassAMember_82c7229d-b606-430f-9514-6ccb6b2388c1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_5c881282-87f8-4f46-9a1f-9326110b688b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_9dc09689-e9b3-47f7-b654-0abe0fda937b" xlink:to="loc_us-gaap_CommonClassBMember_5c881282-87f8-4f46-9a1f-9326110b688b" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.datadoghq.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFSTOCKHOLDERSEQUITY" xlink:type="simple" xlink:href="ddog-20210630.xsd#CONDENSEDCONSOLIDATEDSTATEMENTSOFSTOCKHOLDERSEQUITY"/>
  <link:definitionLink xlink:role="http://www.datadoghq.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFSTOCKHOLDERSEQUITY" xlink:type="extended" id="ia9d57cdf1a5b41b691f604532761166e_CONDENSEDCONSOLIDATEDSTATEMENTSOFSTOCKHOLDERSEQUITY">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_bb9453bd-f2b1-464f-a035-5a913ac8634a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_f2916b20-775f-4141-9c10-71ff9f3e2061" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_bb9453bd-f2b1-464f-a035-5a913ac8634a" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_f2916b20-775f-4141-9c10-71ff9f3e2061" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesOutstanding_790e6535-7c76-4408-8d33-b4a1c09805ed" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_f2916b20-775f-4141-9c10-71ff9f3e2061" xlink:to="loc_us-gaap_SharesOutstanding_790e6535-7c76-4408-8d33-b4a1c09805ed" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_761e5646-654e-436a-aa5c-fffa466e2812" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_f2916b20-775f-4141-9c10-71ff9f3e2061" xlink:to="loc_us-gaap_StockholdersEquity_761e5646-654e-436a-aa5c-fffa466e2812" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_ed470ebb-bca3-4452-827c-78c62185ad63" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_f2916b20-775f-4141-9c10-71ff9f3e2061" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_ed470ebb-bca3-4452-827c-78c62185ad63" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_c123bcbb-5ecc-451b-9e36-e013e0723d99" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_f2916b20-775f-4141-9c10-71ff9f3e2061" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_c123bcbb-5ecc-451b-9e36-e013e0723d99" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_ddog_StockIssuedDuringPeriodValueVestingOfEarlyExercisedStockOptions_a69ff81a-4f84-43dd-bfb0-937cb22d74e8" xlink:href="ddog-20210630.xsd#ddog_StockIssuedDuringPeriodValueVestingOfEarlyExercisedStockOptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_f2916b20-775f-4141-9c10-71ff9f3e2061" xlink:to="loc_ddog_StockIssuedDuringPeriodValueVestingOfEarlyExercisedStockOptions_a69ff81a-4f84-43dd-bfb0-937cb22d74e8" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_ddog_StockIssuedDuringPeriodSharesVestingOfRestrictedStockUnits_22b148fe-fdb4-424a-940b-5da880dc35b2" xlink:href="ddog-20210630.xsd#ddog_StockIssuedDuringPeriodSharesVestingOfRestrictedStockUnits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_f2916b20-775f-4141-9c10-71ff9f3e2061" xlink:to="loc_ddog_StockIssuedDuringPeriodSharesVestingOfRestrictedStockUnits_22b148fe-fdb4-424a-940b-5da880dc35b2" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesAcquisitions_71a9a339-0a14-4e41-b0c0-092ea97a4edf" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesAcquisitions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_f2916b20-775f-4141-9c10-71ff9f3e2061" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesAcquisitions_71a9a339-0a14-4e41-b0c0-092ea97a4edf" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueAcquisitions_0be294e7-4105-499b-bc0d-4dafc34b82d2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueAcquisitions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_f2916b20-775f-4141-9c10-71ff9f3e2061" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueAcquisitions_0be294e7-4105-499b-bc0d-4dafc34b82d2" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_e46fbb9d-0ef6-49ee-bd1a-d1e87673e6f9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_f2916b20-775f-4141-9c10-71ff9f3e2061" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_e46fbb9d-0ef6-49ee-bd1a-d1e87673e6f9" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_9c8a5d46-8df1-4610-a0d2-32f5e8cd3ba4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_f2916b20-775f-4141-9c10-71ff9f3e2061" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_9c8a5d46-8df1-4610-a0d2-32f5e8cd3ba4" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan_a98255ac-562f-4cd7-9c17-01cff83c4975" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_f2916b20-775f-4141-9c10-71ff9f3e2061" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan_a98255ac-562f-4cd7-9c17-01cff83c4975" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalEquityComponentOfConvertibleDebt_e3329a90-4aa6-41f5-b94f-d2bb665fdec9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalEquityComponentOfConvertibleDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_f2916b20-775f-4141-9c10-71ff9f3e2061" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalEquityComponentOfConvertibleDebt_e3329a90-4aa6-41f5-b94f-d2bb665fdec9" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_ddog_AdjustmentsToAdditionalPaidInCapitalPurchasesOfCappedCallsRelatedToConvertibleDebt_95775168-0434-4581-bff6-4efc7c6e253e" xlink:href="ddog-20210630.xsd#ddog_AdjustmentsToAdditionalPaidInCapitalPurchasesOfCappedCallsRelatedToConvertibleDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_f2916b20-775f-4141-9c10-71ff9f3e2061" xlink:to="loc_ddog_AdjustmentsToAdditionalPaidInCapitalPurchasesOfCappedCallsRelatedToConvertibleDebt_95775168-0434-4581-bff6-4efc7c6e253e" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_e67f62de-2d42-41f5-8b5c-f2729f41fee0" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_f2916b20-775f-4141-9c10-71ff9f3e2061" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_e67f62de-2d42-41f5-8b5c-f2729f41fee0" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_8d72a736-2c5f-4437-b159-c475623a8525" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_f2916b20-775f-4141-9c10-71ff9f3e2061" xlink:to="loc_us-gaap_NetIncomeLoss_8d72a736-2c5f-4437-b159-c475623a8525" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountingStandardsUpdateExtensibleList_d35ae9e5-2fce-4fd2-8bb8-ad0f5aa80b24" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AccountingStandardsUpdateExtensibleList"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_f2916b20-775f-4141-9c10-71ff9f3e2061" xlink:to="loc_us-gaap_AccountingStandardsUpdateExtensibleList_d35ae9e5-2fce-4fd2-8bb8-ad0f5aa80b24" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesOutstanding_2be7d27b-54f0-4ed9-bd63-2f3c00b38b6b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_b1d5b2e5-2bf1-4830-a028-a11d7c6ed681" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockholdersEquity"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_8f32eeb2-a854-431d-8303-c34b427da8fc" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_bb9453bd-f2b1-464f-a035-5a913ac8634a" xlink:to="loc_us-gaap_StatementTable_8f32eeb2-a854-431d-8303-c34b427da8fc" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_3573d197-fd19-462f-a696-e228768ae1d4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_8f32eeb2-a854-431d-8303-c34b427da8fc" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_3573d197-fd19-462f-a696-e228768ae1d4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_3573d197-fd19-462f-a696-e228768ae1d4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_3573d197-fd19-462f-a696-e228768ae1d4" xlink:to="loc_us-gaap_EquityComponentDomain_3573d197-fd19-462f-a696-e228768ae1d4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_b0ab39ba-7480-4576-ae52-98e3471a89f2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_3573d197-fd19-462f-a696-e228768ae1d4" xlink:to="loc_us-gaap_EquityComponentDomain_b0ab39ba-7480-4576-ae52-98e3471a89f2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_d766c7c8-47db-41f9-8afa-b112cae38323" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_b0ab39ba-7480-4576-ae52-98e3471a89f2" xlink:to="loc_us-gaap_CommonStockMember_d766c7c8-47db-41f9-8afa-b112cae38323" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_cf3b7e9b-8206-477b-8046-5ddd38bbe7be" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_b0ab39ba-7480-4576-ae52-98e3471a89f2" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_cf3b7e9b-8206-477b-8046-5ddd38bbe7be" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_f7aa4bb2-b441-485e-9f56-fbd128361523" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_b0ab39ba-7480-4576-ae52-98e3471a89f2" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_f7aa4bb2-b441-485e-9f56-fbd128361523" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_bf1a5b88-eea9-4933-ad9c-abac503489a8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_b0ab39ba-7480-4576-ae52-98e3471a89f2" xlink:to="loc_us-gaap_RetainedEarningsMember_bf1a5b88-eea9-4933-ad9c-abac503489a8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CumulativeEffectPeriodOfAdoptionAxis_62c22aa6-4dcf-4291-ba73-59ba6e068532" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_CumulativeEffectPeriodOfAdoptionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_8f32eeb2-a854-431d-8303-c34b427da8fc" xlink:to="loc_srt_CumulativeEffectPeriodOfAdoptionAxis_62c22aa6-4dcf-4291-ba73-59ba6e068532" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CumulativeEffectPeriodOfAdoptionDomain_62c22aa6-4dcf-4291-ba73-59ba6e068532_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_CumulativeEffectPeriodOfAdoptionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CumulativeEffectPeriodOfAdoptionAxis_62c22aa6-4dcf-4291-ba73-59ba6e068532" xlink:to="loc_srt_CumulativeEffectPeriodOfAdoptionDomain_62c22aa6-4dcf-4291-ba73-59ba6e068532_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CumulativeEffectPeriodOfAdoptionDomain_bed65923-c2f8-4f50-933e-91abab8dbe20" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_CumulativeEffectPeriodOfAdoptionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CumulativeEffectPeriodOfAdoptionAxis_62c22aa6-4dcf-4291-ba73-59ba6e068532" xlink:to="loc_srt_CumulativeEffectPeriodOfAdoptionDomain_bed65923-c2f8-4f50-933e-91abab8dbe20" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CumulativeEffectPeriodOfAdoptionAdjustmentMember_9e2369f6-2a68-4ce1-b9b1-f55e72ab3e07" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_CumulativeEffectPeriodOfAdoptionAdjustmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CumulativeEffectPeriodOfAdoptionDomain_bed65923-c2f8-4f50-933e-91abab8dbe20" xlink:to="loc_srt_CumulativeEffectPeriodOfAdoptionAdjustmentMember_9e2369f6-2a68-4ce1-b9b1-f55e72ab3e07" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CumulativeEffectPeriodOfAdoptionAdjustedBalanceMember_bcc28751-260f-4b70-b899-f8b5b6c3629e" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_CumulativeEffectPeriodOfAdoptionAdjustedBalanceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CumulativeEffectPeriodOfAdoptionDomain_bed65923-c2f8-4f50-933e-91abab8dbe20" xlink:to="loc_srt_CumulativeEffectPeriodOfAdoptionAdjustedBalanceMember_bcc28751-260f-4b70-b899-f8b5b6c3629e" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.datadoghq.com/role/BasisofPresentationandSummaryofSignificantAccountingPoliciesDetails" xlink:type="simple" xlink:href="ddog-20210630.xsd#BasisofPresentationandSummaryofSignificantAccountingPoliciesDetails"/>
  <link:definitionLink xlink:role="http://www.datadoghq.com/role/BasisofPresentationandSummaryofSignificantAccountingPoliciesDetails" xlink:type="extended" id="i207a1e8f5e434f8bb0410caf33a217fb_BasisofPresentationandSummaryofSignificantAccountingPoliciesDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems_2b611c12-a7fd-4420-9e03-f29c3d453056" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_104cf488-1476-404e-be43-01f347194e95" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems_2b611c12-a7fd-4420-9e03-f29c3d453056" xlink:to="loc_us-gaap_StockholdersEquity_104cf488-1476-404e-be43-01f347194e95" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleLongTermNotesPayable_f0033157-9ac5-45e6-b642-7c5fc087039e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConvertibleLongTermNotesPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems_2b611c12-a7fd-4420-9e03-f29c3d453056" xlink:to="loc_us-gaap_ConvertibleLongTermNotesPayable_f0033157-9ac5-45e6-b642-7c5fc087039e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable_7e792e4a-a835-4442-8d95-63bfdf602053" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleLineItems_2b611c12-a7fd-4420-9e03-f29c3d453056" xlink:to="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable_7e792e4a-a835-4442-8d95-63bfdf602053" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_fe5d288a-ec27-4ad1-a9aa-f21a365bba41" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable_7e792e4a-a835-4442-8d95-63bfdf602053" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_fe5d288a-ec27-4ad1-a9aa-f21a365bba41" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_fe5d288a-ec27-4ad1-a9aa-f21a365bba41_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_fe5d288a-ec27-4ad1-a9aa-f21a365bba41" xlink:to="loc_us-gaap_EquityComponentDomain_fe5d288a-ec27-4ad1-a9aa-f21a365bba41_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_b55db9cc-34eb-43a0-984b-4ce2a2584c36" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_fe5d288a-ec27-4ad1-a9aa-f21a365bba41" xlink:to="loc_us-gaap_EquityComponentDomain_b55db9cc-34eb-43a0-984b-4ce2a2584c36" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_720a402f-3d37-4e7f-9511-e9db71478e70" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_b55db9cc-34eb-43a0-984b-4ce2a2584c36" xlink:to="loc_us-gaap_RetainedEarningsMember_720a402f-3d37-4e7f-9511-e9db71478e70" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_d7e3cf63-6cf9-41fc-9f60-80622b07e4d2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_b55db9cc-34eb-43a0-984b-4ce2a2584c36" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_d7e3cf63-6cf9-41fc-9f60-80622b07e4d2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CumulativeEffectPeriodOfAdoptionAxis_7af85243-c9dc-484c-b3e6-f7f2748f939e" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_CumulativeEffectPeriodOfAdoptionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable_7e792e4a-a835-4442-8d95-63bfdf602053" xlink:to="loc_srt_CumulativeEffectPeriodOfAdoptionAxis_7af85243-c9dc-484c-b3e6-f7f2748f939e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CumulativeEffectPeriodOfAdoptionDomain_7af85243-c9dc-484c-b3e6-f7f2748f939e_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_CumulativeEffectPeriodOfAdoptionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CumulativeEffectPeriodOfAdoptionAxis_7af85243-c9dc-484c-b3e6-f7f2748f939e" xlink:to="loc_srt_CumulativeEffectPeriodOfAdoptionDomain_7af85243-c9dc-484c-b3e6-f7f2748f939e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CumulativeEffectPeriodOfAdoptionDomain_2f7aa7e8-14e1-453b-9ed3-46869dca0837" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_CumulativeEffectPeriodOfAdoptionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CumulativeEffectPeriodOfAdoptionAxis_7af85243-c9dc-484c-b3e6-f7f2748f939e" xlink:to="loc_srt_CumulativeEffectPeriodOfAdoptionDomain_2f7aa7e8-14e1-453b-9ed3-46869dca0837" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CumulativeEffectPeriodOfAdoptionAdjustmentMember_92ab0c1b-8d02-4b63-81f3-bdeec2d5482d" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_CumulativeEffectPeriodOfAdoptionAdjustmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CumulativeEffectPeriodOfAdoptionDomain_2f7aa7e8-14e1-453b-9ed3-46869dca0837" xlink:to="loc_srt_CumulativeEffectPeriodOfAdoptionAdjustmentMember_92ab0c1b-8d02-4b63-81f3-bdeec2d5482d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_6918e9c7-63a2-4290-be6a-a41ed6adc95b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AdjustmentsForNewAccountingPronouncementsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_NewAccountingPronouncementsOrChangeInAccountingPrincipleTable_7e792e4a-a835-4442-8d95-63bfdf602053" xlink:to="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_6918e9c7-63a2-4290-be6a-a41ed6adc95b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfAdoptionMember_6918e9c7-63a2-4290-be6a-a41ed6adc95b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TypeOfAdoptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_6918e9c7-63a2-4290-be6a-a41ed6adc95b" xlink:to="loc_us-gaap_TypeOfAdoptionMember_6918e9c7-63a2-4290-be6a-a41ed6adc95b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfAdoptionMember_1bfeabda-b9fb-4691-b0ef-d3c7fcbbbee1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TypeOfAdoptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_6918e9c7-63a2-4290-be6a-a41ed6adc95b" xlink:to="loc_us-gaap_TypeOfAdoptionMember_1bfeabda-b9fb-4691-b0ef-d3c7fcbbbee1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountingStandardsUpdate202006Member_8abe9c9c-743b-4175-8683-a6d339c52fc7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AccountingStandardsUpdate202006Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfAdoptionMember_1bfeabda-b9fb-4691-b0ef-d3c7fcbbbee1" xlink:to="loc_us-gaap_AccountingStandardsUpdate202006Member_8abe9c9c-743b-4175-8683-a6d339c52fc7" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.datadoghq.com/role/MarketableSecuritiesSummaryofAvailableforsaleMarketableSecuritiesDetails" xlink:type="simple" xlink:href="ddog-20210630.xsd#MarketableSecuritiesSummaryofAvailableforsaleMarketableSecuritiesDetails"/>
  <link:definitionLink xlink:role="http://www.datadoghq.com/role/MarketableSecuritiesSummaryofAvailableforsaleMarketableSecuritiesDetails" xlink:type="extended" id="ia37e3c98302c4f9a9a9376263572b46a_MarketableSecuritiesSummaryofAvailableforsaleMarketableSecuritiesDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MarketableSecuritiesLineItems_4904dd82-e885-4d9b-b5c1-5a289f96a1ea" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_MarketableSecuritiesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_f66161cf-8f1e-4a4c-ba47-084efbcfa610" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_4904dd82-e885-4d9b-b5c1-5a289f96a1ea" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_f66161cf-8f1e-4a4c-ba47-084efbcfa610" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_0b8e2e45-1859-4ef1-b6cc-1eda04daa76d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_4904dd82-e885-4d9b-b5c1-5a289f96a1ea" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_0b8e2e45-1859-4ef1-b6cc-1eda04daa76d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_81b55f02-8baa-4395-8aef-d70fed538622" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_4904dd82-e885-4d9b-b5c1-5a289f96a1ea" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_81b55f02-8baa-4395-8aef-d70fed538622" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_05f7db4d-d7ce-48ee-a694-b514337609fa" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_4904dd82-e885-4d9b-b5c1-5a289f96a1ea" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_05f7db4d-d7ce-48ee-a694-b514337609fa" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MarketableSecuritiesTable_bc6ab840-0497-40d8-8686-2cc71d231377" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_MarketableSecuritiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_4904dd82-e885-4d9b-b5c1-5a289f96a1ea" xlink:to="loc_us-gaap_MarketableSecuritiesTable_bc6ab840-0497-40d8-8686-2cc71d231377" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_f28377c8-f992-40f0-bd2a-657a568447eb" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_MarketableSecuritiesTable_bc6ab840-0497-40d8-8686-2cc71d231377" xlink:to="loc_us-gaap_FinancialInstrumentAxis_f28377c8-f992-40f0-bd2a-657a568447eb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_f28377c8-f992-40f0-bd2a-657a568447eb_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_f28377c8-f992-40f0-bd2a-657a568447eb" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_f28377c8-f992-40f0-bd2a-657a568447eb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_0bc15430-8b3c-4dd6-86f8-0f05379428ce" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_f28377c8-f992-40f0-bd2a-657a568447eb" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_0bc15430-8b3c-4dd6-86f8-0f05379428ce" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ddog_CommercialDebtSecurityMember_3edb131e-e789-47a5-bc99-7cb9cac15032" xlink:href="ddog-20210630.xsd#ddog_CommercialDebtSecurityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_0bc15430-8b3c-4dd6-86f8-0f05379428ce" xlink:to="loc_ddog_CommercialDebtSecurityMember_3edb131e-e789-47a5-bc99-7cb9cac15032" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CertificatesOfDepositMember_9018546c-ab70-43ad-8baf-c59ce2de6aa7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CertificatesOfDepositMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_0bc15430-8b3c-4dd6-86f8-0f05379428ce" xlink:to="loc_us-gaap_CertificatesOfDepositMember_9018546c-ab70-43ad-8baf-c59ce2de6aa7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USTreasurySecuritiesMember_840c7bfe-9815-4cbb-87b1-f2d18214d2e7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_USTreasurySecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_0bc15430-8b3c-4dd6-86f8-0f05379428ce" xlink:to="loc_us-gaap_USTreasurySecuritiesMember_840c7bfe-9815-4cbb-87b1-f2d18214d2e7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialPaperMember_fb931048-0632-440f-b559-385df78e50d5" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommercialPaperMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_0bc15430-8b3c-4dd6-86f8-0f05379428ce" xlink:to="loc_us-gaap_CommercialPaperMember_fb931048-0632-440f-b559-385df78e50d5" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.datadoghq.com/role/FairValueMeasurementsSummaryofFinancialAssetsandLiabilitiesMeasuredatFairValueonRecurringBasisDetails" xlink:type="simple" xlink:href="ddog-20210630.xsd#FairValueMeasurementsSummaryofFinancialAssetsandLiabilitiesMeasuredatFairValueonRecurringBasisDetails"/>
  <link:definitionLink xlink:role="http://www.datadoghq.com/role/FairValueMeasurementsSummaryofFinancialAssetsandLiabilitiesMeasuredatFairValueonRecurringBasisDetails" xlink:type="extended" id="ia4f54d9b00f046008ce3108de687e7b8_FairValueMeasurementsSummaryofFinancialAssetsandLiabilitiesMeasuredatFairValueonRecurringBasisDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_6f20b78a-7e7e-4a97-ad0a-75893db90103" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosureAbstract_a93ee41d-4c9c-43c7-9f82-f9107df6b0ee" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AssetsFairValueDisclosureAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_6f20b78a-7e7e-4a97-ad0a-75893db90103" xlink:to="loc_us-gaap_AssetsFairValueDisclosureAbstract_a93ee41d-4c9c-43c7-9f82-f9107df6b0ee" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_ab08c057-ae75-46d4-9523-188f5e9c0740" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CashAndCashEquivalentsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_a93ee41d-4c9c-43c7-9f82-f9107df6b0ee" xlink:to="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_ab08c057-ae75-46d4-9523-188f5e9c0740" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_8996a479-ddc1-442f-9df2-35b2378df477" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_a93ee41d-4c9c-43c7-9f82-f9107df6b0ee" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_8996a479-ddc1-442f-9df2-35b2378df477" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosure_a21c7622-4452-40fb-a89c-0ed50aef2ae8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AssetsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_a93ee41d-4c9c-43c7-9f82-f9107df6b0ee" xlink:to="loc_us-gaap_AssetsFairValueDisclosure_a21c7622-4452-40fb-a89c-0ed50aef2ae8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_a0113716-086c-485d-aa52-a4b122fa6fd7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_6f20b78a-7e7e-4a97-ad0a-75893db90103" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_a0113716-086c-485d-aa52-a4b122fa6fd7" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementFrequencyAxis_9cd63dbb-104d-4011-b263-a96ec10e242e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueByMeasurementFrequencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_a0113716-086c-485d-aa52-a4b122fa6fd7" xlink:to="loc_us-gaap_FairValueByMeasurementFrequencyAxis_9cd63dbb-104d-4011-b263-a96ec10e242e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_9cd63dbb-104d-4011-b263-a96ec10e242e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_9cd63dbb-104d-4011-b263-a96ec10e242e" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_9cd63dbb-104d-4011-b263-a96ec10e242e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementFrequencyDomain_2be3c3f2-a0e3-4b04-a031-fc81b1b41634" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueMeasurementFrequencyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementFrequencyAxis_9cd63dbb-104d-4011-b263-a96ec10e242e" xlink:to="loc_us-gaap_FairValueMeasurementFrequencyDomain_2be3c3f2-a0e3-4b04-a031-fc81b1b41634" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsRecurringMember_82b2bcfc-f9b1-4388-bfb6-c58131c8efda" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueMeasurementsRecurringMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementFrequencyDomain_2be3c3f2-a0e3-4b04-a031-fc81b1b41634" xlink:to="loc_us-gaap_FairValueMeasurementsRecurringMember_82b2bcfc-f9b1-4388-bfb6-c58131c8efda" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_31a91469-a2b7-4725-b7c3-46fbd3336ede" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_a0113716-086c-485d-aa52-a4b122fa6fd7" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_31a91469-a2b7-4725-b7c3-46fbd3336ede" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_31a91469-a2b7-4725-b7c3-46fbd3336ede_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_31a91469-a2b7-4725-b7c3-46fbd3336ede" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_31a91469-a2b7-4725-b7c3-46fbd3336ede_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_86f59c0b-9b23-4720-b501-a8ec8ca18ef9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_31a91469-a2b7-4725-b7c3-46fbd3336ede" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_86f59c0b-9b23-4720-b501-a8ec8ca18ef9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_39fa09ca-7723-451a-8a39-efa5f7204ebe" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_86f59c0b-9b23-4720-b501-a8ec8ca18ef9" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_39fa09ca-7723-451a-8a39-efa5f7204ebe" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_9f48f6b4-55a5-49d4-9547-2b39b6f16526" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_86f59c0b-9b23-4720-b501-a8ec8ca18ef9" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_9f48f6b4-55a5-49d4-9547-2b39b6f16526" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_423ce9e9-8ed6-455d-a3d5-84979fb98d34" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_86f59c0b-9b23-4720-b501-a8ec8ca18ef9" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_423ce9e9-8ed6-455d-a3d5-84979fb98d34" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_fceaeeb1-074c-4e71-81af-24a2f2a09a0a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_a0113716-086c-485d-aa52-a4b122fa6fd7" xlink:to="loc_us-gaap_FinancialInstrumentAxis_fceaeeb1-074c-4e71-81af-24a2f2a09a0a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_fceaeeb1-074c-4e71-81af-24a2f2a09a0a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_fceaeeb1-074c-4e71-81af-24a2f2a09a0a" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_fceaeeb1-074c-4e71-81af-24a2f2a09a0a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_f4c6dd66-f645-433b-a745-994f86cb3e7f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_fceaeeb1-074c-4e71-81af-24a2f2a09a0a" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_f4c6dd66-f645-433b-a745-994f86cb3e7f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MoneyMarketFundsMember_eb37ec6d-3714-49ba-9df3-99750ed8e255" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_MoneyMarketFundsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_f4c6dd66-f645-433b-a745-994f86cb3e7f" xlink:to="loc_us-gaap_MoneyMarketFundsMember_eb37ec6d-3714-49ba-9df3-99750ed8e255" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateDebtSecuritiesMember_eb8e98fd-8f58-4c7a-9ad1-4012209afb34" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CorporateDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_f4c6dd66-f645-433b-a745-994f86cb3e7f" xlink:to="loc_us-gaap_CorporateDebtSecuritiesMember_eb8e98fd-8f58-4c7a-9ad1-4012209afb34" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CertificatesOfDepositMember_684479a7-33ca-4706-9bb9-8a237498ba9d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CertificatesOfDepositMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_f4c6dd66-f645-433b-a745-994f86cb3e7f" xlink:to="loc_us-gaap_CertificatesOfDepositMember_684479a7-33ca-4706-9bb9-8a237498ba9d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USTreasuryAndGovernmentMember_4b5f75d4-199a-4aa9-a32a-bb45347b2ee2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_USTreasuryAndGovernmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_f4c6dd66-f645-433b-a745-994f86cb3e7f" xlink:to="loc_us-gaap_USTreasuryAndGovernmentMember_4b5f75d4-199a-4aa9-a32a-bb45347b2ee2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialPaperMember_d256f8b2-e295-47cc-a01b-c398de8f88d7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommercialPaperMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_f4c6dd66-f645-433b-a745-994f86cb3e7f" xlink:to="loc_us-gaap_CommercialPaperMember_d256f8b2-e295-47cc-a01b-c398de8f88d7" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.datadoghq.com/role/PropertyandEquipmentNetComponentsofPropertyandEquipmentNetDetails" xlink:type="simple" xlink:href="ddog-20210630.xsd#PropertyandEquipmentNetComponentsofPropertyandEquipmentNetDetails"/>
  <link:definitionLink xlink:role="http://www.datadoghq.com/role/PropertyandEquipmentNetComponentsofPropertyandEquipmentNetDetails" xlink:type="extended" id="i2f6e942c2bbd4e43b875495b17455e2d_PropertyandEquipmentNetComponentsofPropertyandEquipmentNetDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_6159e3f3-e14a-461b-b8f7-9245a348de40" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentGross_6493c02f-8b2c-4d40-8b6c-5da24ab0a30e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PropertyPlantAndEquipmentGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_6159e3f3-e14a-461b-b8f7-9245a348de40" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentGross_6493c02f-8b2c-4d40-8b6c-5da24ab0a30e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_5e6f07ca-4feb-49f4-9e78-8aef5e7a4ffa" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_6159e3f3-e14a-461b-b8f7-9245a348de40" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_5e6f07ca-4feb-49f4-9e78-8aef5e7a4ffa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_4c993446-f02c-47be-96fa-ae8d6b48cf1a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_6159e3f3-e14a-461b-b8f7-9245a348de40" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_4c993446-f02c-47be-96fa-ae8d6b48cf1a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_823d8274-0b69-4280-b1d5-83f32dc94b4b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_6159e3f3-e14a-461b-b8f7-9245a348de40" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_823d8274-0b69-4280-b1d5-83f32dc94b4b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_bcd8e875-4406-45c1-8cbe-81af6efe154f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_823d8274-0b69-4280-b1d5-83f32dc94b4b" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_bcd8e875-4406-45c1-8cbe-81af6efe154f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_bcd8e875-4406-45c1-8cbe-81af6efe154f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_bcd8e875-4406-45c1-8cbe-81af6efe154f" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_bcd8e875-4406-45c1-8cbe-81af6efe154f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_744bb0c7-ab52-482c-b95e-b7f7fb9edc64" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_bcd8e875-4406-45c1-8cbe-81af6efe154f" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_744bb0c7-ab52-482c-b95e-b7f7fb9edc64" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComputerEquipmentMember_01bfb291-d175-40d3-85f6-758935cbfe83" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ComputerEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_744bb0c7-ab52-482c-b95e-b7f7fb9edc64" xlink:to="loc_us-gaap_ComputerEquipmentMember_01bfb291-d175-40d3-85f6-758935cbfe83" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FurnitureAndFixturesMember_ac5d1dd4-c5d5-4270-8e90-db2b191337cf" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FurnitureAndFixturesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_744bb0c7-ab52-482c-b95e-b7f7fb9edc64" xlink:to="loc_us-gaap_FurnitureAndFixturesMember_ac5d1dd4-c5d5-4270-8e90-db2b191337cf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LeaseholdImprovementsMember_26b72813-e9c7-4622-9dc2-f947afd97124" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LeaseholdImprovementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_744bb0c7-ab52-482c-b95e-b7f7fb9edc64" xlink:to="loc_us-gaap_LeaseholdImprovementsMember_26b72813-e9c7-4622-9dc2-f947afd97124" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SoftwareAndSoftwareDevelopmentCostsMember_112970ee-732e-40c3-a050-440de8bda953" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SoftwareAndSoftwareDevelopmentCostsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_744bb0c7-ab52-482c-b95e-b7f7fb9edc64" xlink:to="loc_us-gaap_SoftwareAndSoftwareDevelopmentCostsMember_112970ee-732e-40c3-a050-440de8bda953" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.datadoghq.com/role/AcquisitionIntangibleAssetsandGoodwillAdditionalInformationDetails" xlink:type="simple" xlink:href="ddog-20210630.xsd#AcquisitionIntangibleAssetsandGoodwillAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://www.datadoghq.com/role/AcquisitionIntangibleAssetsandGoodwillAdditionalInformationDetails" xlink:type="extended" id="i71a6c72d70a049e28820bd786f136d5b_AcquisitionIntangibleAssetsandGoodwillAdditionalInformationDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionLineItems_91117fee-3649-4443-b245-7f6c9ada858e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessAcquisitionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferred1_770f0796-45a0-4e49-92b0-7d82bfd273c7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessCombinationConsiderationTransferred1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_91117fee-3649-4443-b245-7f6c9ada858e" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferred1_770f0796-45a0-4e49-92b0-7d82bfd273c7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill_970e9bf1-6439-4a26-b107-c4968def3ff0" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_91117fee-3649-4443-b245-7f6c9ada858e" xlink:to="loc_us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill_970e9bf1-6439-4a26-b107-c4968def3ff0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_6884390c-84f7-4a20-bc20-631ee90c590a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_91117fee-3649-4443-b245-7f6c9ada858e" xlink:to="loc_us-gaap_Goodwill_6884390c-84f7-4a20-bc20-631ee90c590a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife_eadab75d-04eb-41ae-9b47-10188a7e0bfe" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_91117fee-3649-4443-b245-7f6c9ada858e" xlink:to="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife_eadab75d-04eb-41ae-9b47-10188a7e0bfe" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeveranceCosts1_0738476b-c101-4a53-8599-1b782cd554fd" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SeveranceCosts1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_91117fee-3649-4443-b245-7f6c9ada858e" xlink:to="loc_us-gaap_SeveranceCosts1_0738476b-c101-4a53-8599-1b782cd554fd" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfIntangibleAssets_611c1a78-721f-4819-bdc4-25802b083518" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AmortizationOfIntangibleAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_91117fee-3649-4443-b245-7f6c9ada858e" xlink:to="loc_us-gaap_AmortizationOfIntangibleAssets_611c1a78-721f-4819-bdc4-25802b083518" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_dbeba501-7602-400b-98aa-65bc437bd9c3" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionLineItems_91117fee-3649-4443-b245-7f6c9ada858e" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_dbeba501-7602-400b-98aa-65bc437bd9c3" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_1fc5a4da-d027-44bd-bb23-004717f005c4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_dbeba501-7602-400b-98aa-65bc437bd9c3" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_1fc5a4da-d027-44bd-bb23-004717f005c4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_1fc5a4da-d027-44bd-bb23-004717f005c4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_1fc5a4da-d027-44bd-bb23-004717f005c4" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_1fc5a4da-d027-44bd-bb23-004717f005c4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_3eb5147b-6c72-4c86-bd89-95af01b8f1e4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_1fc5a4da-d027-44bd-bb23-004717f005c4" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_3eb5147b-6c72-4c86-bd89-95af01b8f1e4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ddog_AcquisitionInApril2021Member_eb5ccc87-7341-4f7d-893f-e21ee83acaa4" xlink:href="ddog-20210630.xsd#ddog_AcquisitionInApril2021Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_3eb5147b-6c72-4c86-bd89-95af01b8f1e4" xlink:to="loc_ddog_AcquisitionInApril2021Member_eb5ccc87-7341-4f7d-893f-e21ee83acaa4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ddog_AcquisitionInFebruary2021Member_31090bfa-7777-4063-8b73-9a43b8a2a83a" xlink:href="ddog-20210630.xsd#ddog_AcquisitionInFebruary2021Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_3eb5147b-6c72-4c86-bd89-95af01b8f1e4" xlink:to="loc_ddog_AcquisitionInFebruary2021Member_31090bfa-7777-4063-8b73-9a43b8a2a83a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ddog_TwoThousandTwentyAcquisitionMember_acb02a7d-73d5-4069-9e37-a8bb75c82b6b" xlink:href="ddog-20210630.xsd#ddog_TwoThousandTwentyAcquisitionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_3eb5147b-6c72-4c86-bd89-95af01b8f1e4" xlink:to="loc_ddog_TwoThousandTwentyAcquisitionMember_acb02a7d-73d5-4069-9e37-a8bb75c82b6b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_1d251b53-3761-449a-aa8d-0cbc7eda7f66" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_dbeba501-7602-400b-98aa-65bc437bd9c3" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_1d251b53-3761-449a-aa8d-0cbc7eda7f66" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_1d251b53-3761-449a-aa8d-0cbc7eda7f66_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_1d251b53-3761-449a-aa8d-0cbc7eda7f66" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_1d251b53-3761-449a-aa8d-0cbc7eda7f66_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_34e046c3-563d-45ba-96b0-daec3a1a064a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_1d251b53-3761-449a-aa8d-0cbc7eda7f66" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_34e046c3-563d-45ba-96b0-daec3a1a064a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DevelopedTechnologyRightsMember_ccd5787c-ef96-4867-ac25-5c16beacd5bb" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DevelopedTechnologyRightsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_34e046c3-563d-45ba-96b0-daec3a1a064a" xlink:to="loc_us-gaap_DevelopedTechnologyRightsMember_ccd5787c-ef96-4867-ac25-5c16beacd5bb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerRelationshipsMember_ffcb743f-647d-4265-9b0e-2f11acd25eed" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CustomerRelationshipsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_34e046c3-563d-45ba-96b0-daec3a1a064a" xlink:to="loc_us-gaap_CustomerRelationshipsMember_ffcb743f-647d-4265-9b0e-2f11acd25eed" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.datadoghq.com/role/AcquisitionIntangibleAssetsandGoodwillScheduleofIntangibleAssetsNetDetails" xlink:type="simple" xlink:href="ddog-20210630.xsd#AcquisitionIntangibleAssetsandGoodwillScheduleofIntangibleAssetsNetDetails"/>
  <link:definitionLink xlink:role="http://www.datadoghq.com/role/AcquisitionIntangibleAssetsandGoodwillScheduleofIntangibleAssetsNetDetails" xlink:type="extended" id="i1f1bc1b1c8ee4ea5b4189f8551e09457_AcquisitionIntangibleAssetsandGoodwillScheduleofIntangibleAssetsNetDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_33663d01-d9bd-44f9-8ae2-d53338209275" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsGross_796896c9-9f3b-4487-9079-aa9812ed510d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_33663d01-d9bd-44f9-8ae2-d53338209275" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsGross_796896c9-9f3b-4487-9079-aa9812ed510d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_b9d94e33-eba3-4703-a38b-cfbc10ecfbaa" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_33663d01-d9bd-44f9-8ae2-d53338209275" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_b9d94e33-eba3-4703-a38b-cfbc10ecfbaa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_35f77cf0-d519-4aca-a996-d393ab0ff5aa" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_33663d01-d9bd-44f9-8ae2-d53338209275" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_35f77cf0-d519-4aca-a996-d393ab0ff5aa" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsRemainingAmortizationPeriod1_3b5def62-8f62-42b4-8880-e83f216197ce" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsRemainingAmortizationPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_33663d01-d9bd-44f9-8ae2-d53338209275" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsRemainingAmortizationPeriod1_3b5def62-8f62-42b4-8880-e83f216197ce" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_283c1c5c-e2de-406d-b0f0-20de1cc3a341" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_33663d01-d9bd-44f9-8ae2-d53338209275" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_283c1c5c-e2de-406d-b0f0-20de1cc3a341" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_a03649ee-b43d-4cbb-85ea-ffd786d84b27" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_283c1c5c-e2de-406d-b0f0-20de1cc3a341" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_a03649ee-b43d-4cbb-85ea-ffd786d84b27" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_a03649ee-b43d-4cbb-85ea-ffd786d84b27_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_a03649ee-b43d-4cbb-85ea-ffd786d84b27" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_a03649ee-b43d-4cbb-85ea-ffd786d84b27_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_c5e94c68-e066-4341-8157-0357bae7a1f3" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_a03649ee-b43d-4cbb-85ea-ffd786d84b27" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_c5e94c68-e066-4341-8157-0357bae7a1f3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DevelopedTechnologyRightsMember_30e3102a-0117-42e9-88df-e423e32c7c7d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DevelopedTechnologyRightsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_c5e94c68-e066-4341-8157-0357bae7a1f3" xlink:to="loc_us-gaap_DevelopedTechnologyRightsMember_30e3102a-0117-42e9-88df-e423e32c7c7d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerRelationshipsMember_803c00b0-ff3b-4268-a1ae-beac02f36a20" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CustomerRelationshipsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_c5e94c68-e066-4341-8157-0357bae7a1f3" xlink:to="loc_us-gaap_CustomerRelationshipsMember_803c00b0-ff3b-4268-a1ae-beac02f36a20" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.datadoghq.com/role/ConvertibleSeniorNotesAdditionalInformationDetails" xlink:type="simple" xlink:href="ddog-20210630.xsd#ConvertibleSeniorNotesAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://www.datadoghq.com/role/ConvertibleSeniorNotesAdditionalInformationDetails" xlink:type="extended" id="i9776a8c5e11145269c6f5d4141ecfc32_ConvertibleSeniorNotesAdditionalInformationDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_ded538fa-0783-41e9-acfd-4f21b01396dd" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_91a5a310-ac9d-4a36-98cd-4521ae8ddf30" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_ded538fa-0783-41e9-acfd-4f21b01396dd" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_91a5a310-ac9d-4a36-98cd-4521ae8ddf30" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_17d72ecb-3944-4d7b-9fb2-c3b6ae316ff5" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_ded538fa-0783-41e9-acfd-4f21b01396dd" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_17d72ecb-3944-4d7b-9fb2-c3b6ae316ff5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromConvertibleDebt_02901b9e-a3b7-49a4-a741-2b125c56b917" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ProceedsFromConvertibleDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_ded538fa-0783-41e9-acfd-4f21b01396dd" xlink:to="loc_us-gaap_ProceedsFromConvertibleDebt_02901b9e-a3b7-49a4-a741-2b125c56b917" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleThresholdTradingDays_b667aa40-3724-4bd3-a6fa-520e83ea3f17" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentConvertibleThresholdTradingDays"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_ded538fa-0783-41e9-acfd-4f21b01396dd" xlink:to="loc_us-gaap_DebtInstrumentConvertibleThresholdTradingDays_b667aa40-3724-4bd3-a6fa-520e83ea3f17" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleThresholdConsecutiveTradingDays1_a6ade960-5d14-4a10-a92f-e4d26007d830" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentConvertibleThresholdConsecutiveTradingDays1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_ded538fa-0783-41e9-acfd-4f21b01396dd" xlink:to="loc_us-gaap_DebtInstrumentConvertibleThresholdConsecutiveTradingDays1_a6ade960-5d14-4a10-a92f-e4d26007d830" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleThresholdPercentageOfStockPriceTrigger_83cebfff-6885-4be2-affd-7963a59ae8f9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentConvertibleThresholdPercentageOfStockPriceTrigger"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_ded538fa-0783-41e9-acfd-4f21b01396dd" xlink:to="loc_us-gaap_DebtInstrumentConvertibleThresholdPercentageOfStockPriceTrigger_83cebfff-6885-4be2-affd-7963a59ae8f9" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_ddog_DebtInstrumentConvertibleThresholdBusinessDays_dcc1c55a-a848-4284-9d49-54db3deebf56" xlink:href="ddog-20210630.xsd#ddog_DebtInstrumentConvertibleThresholdBusinessDays"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_ded538fa-0783-41e9-acfd-4f21b01396dd" xlink:to="loc_ddog_DebtInstrumentConvertibleThresholdBusinessDays_dcc1c55a-a848-4284-9d49-54db3deebf56" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_ddog_DebtInstrumentFairValueCalculationBase_80ba5b87-af9b-471e-b34c-6842166c8dd3" xlink:href="ddog-20210630.xsd#ddog_DebtInstrumentFairValueCalculationBase"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_ded538fa-0783-41e9-acfd-4f21b01396dd" xlink:to="loc_ddog_DebtInstrumentFairValueCalculationBase_80ba5b87-af9b-471e-b34c-6842166c8dd3" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_ddog_DebtInstrumentConvertibleThresholdMaximumPercentageOfProductOfLastReportedSalePriceOfCommonStock_f76bdaa3-dff2-4a31-baf7-ffefaebb3901" xlink:href="ddog-20210630.xsd#ddog_DebtInstrumentConvertibleThresholdMaximumPercentageOfProductOfLastReportedSalePriceOfCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_ded538fa-0783-41e9-acfd-4f21b01396dd" xlink:to="loc_ddog_DebtInstrumentConvertibleThresholdMaximumPercentageOfProductOfLastReportedSalePriceOfCommonStock_f76bdaa3-dff2-4a31-baf7-ffefaebb3901" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleConversionRatio1_16c39b28-148d-4fa8-86ed-4ba41d82d3cc" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentConvertibleConversionRatio1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_ded538fa-0783-41e9-acfd-4f21b01396dd" xlink:to="loc_us-gaap_DebtInstrumentConvertibleConversionRatio1_16c39b28-148d-4fa8-86ed-4ba41d82d3cc" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleConversionPrice1_80aa0094-ca90-414a-be91-f6d97a3a19bc" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentConvertibleConversionPrice1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_ded538fa-0783-41e9-acfd-4f21b01396dd" xlink:to="loc_us-gaap_DebtInstrumentConvertibleConversionPrice1_80aa0094-ca90-414a-be91-f6d97a3a19bc" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPricePercentageOfPrincipalAmountRedeemed_ac77de84-7e90-411e-801e-0c8eed9dd07f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentRedemptionPricePercentageOfPrincipalAmountRedeemed"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_ded538fa-0783-41e9-acfd-4f21b01396dd" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPricePercentageOfPrincipalAmountRedeemed_ac77de84-7e90-411e-801e-0c8eed9dd07f" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_ddog_DebtInstrumentDiscountForConversionOption_78591fed-418a-4a08-bb40-1be9a2922525" xlink:href="ddog-20210630.xsd#ddog_DebtInstrumentDiscountForConversionOption"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_ded538fa-0783-41e9-acfd-4f21b01396dd" xlink:to="loc_ddog_DebtInstrumentDiscountForConversionOption_78591fed-418a-4a08-bb40-1be9a2922525" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredFinanceCostsNet_dfeabe23-e2fb-4a5b-9530-b296dbc83d6a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DeferredFinanceCostsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_ded538fa-0783-41e9-acfd-4f21b01396dd" xlink:to="loc_us-gaap_DeferredFinanceCostsNet_dfeabe23-e2fb-4a5b-9530-b296dbc83d6a" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_ddog_DebtIssuanceCostAttributableToLiabilityComponent_6a019174-6cf6-4499-9dc8-fa0dd10d8a6a" xlink:href="ddog-20210630.xsd#ddog_DebtIssuanceCostAttributableToLiabilityComponent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_ded538fa-0783-41e9-acfd-4f21b01396dd" xlink:to="loc_ddog_DebtIssuanceCostAttributableToLiabilityComponent_6a019174-6cf6-4499-9dc8-fa0dd10d8a6a" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_455b2dc0-eb84-4202-bdb0-646089a28ef0" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentInterestRateEffectivePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_ded538fa-0783-41e9-acfd-4f21b01396dd" xlink:to="loc_us-gaap_DebtInstrumentInterestRateEffectivePercentage_455b2dc0-eb84-4202-bdb0-646089a28ef0" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_ddog_DebtIssuanceCostAttributableToEquityComponent_05719623-dbb8-424c-8d54-64b680c71a23" xlink:href="ddog-20210630.xsd#ddog_DebtIssuanceCostAttributableToEquityComponent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_ded538fa-0783-41e9-acfd-4f21b01396dd" xlink:to="loc_ddog_DebtIssuanceCostAttributableToEquityComponent_05719623-dbb8-424c-8d54-64b680c71a23" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_a737082f-61f4-437d-8acb-91392811ba34" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_ded538fa-0783-41e9-acfd-4f21b01396dd" xlink:to="loc_us-gaap_StockholdersEquity_a737082f-61f4-437d-8acb-91392811ba34" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleLongTermNotesPayable_4d22e365-9b66-4bd6-b717-a69a4852cb21" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConvertibleLongTermNotesPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_ded538fa-0783-41e9-acfd-4f21b01396dd" xlink:to="loc_us-gaap_ConvertibleLongTermNotesPayable_4d22e365-9b66-4bd6-b717-a69a4852cb21" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtFairValue_fb019a1c-ee51-4f43-9105-541b1609c804" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_LongTermDebtFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_ded538fa-0783-41e9-acfd-4f21b01396dd" xlink:to="loc_us-gaap_LongTermDebtFairValue_fb019a1c-ee51-4f43-9105-541b1609c804" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleStockPriceTrigger_d527eb08-44b9-41fe-b47e-0861d8805f9c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentConvertibleStockPriceTrigger"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_ded538fa-0783-41e9-acfd-4f21b01396dd" xlink:to="loc_us-gaap_DebtInstrumentConvertibleStockPriceTrigger_d527eb08-44b9-41fe-b47e-0861d8805f9c" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_ddog_InitialCapPricePerShareOfCappedCalls_425bdacb-305c-4278-b903-a749ccb089b5" xlink:href="ddog-20210630.xsd#ddog_InitialCapPricePerShareOfCappedCalls"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_ded538fa-0783-41e9-acfd-4f21b01396dd" xlink:to="loc_ddog_InitialCapPricePerShareOfCappedCalls_425bdacb-305c-4278-b903-a749ccb089b5" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_ddog_CommonStockCoveredUnderCappedCallsTransaction_4aea9f53-155b-4244-83c2-93a179a2e2dd" xlink:href="ddog-20210630.xsd#ddog_CommonStockCoveredUnderCappedCallsTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_ded538fa-0783-41e9-acfd-4f21b01396dd" xlink:to="loc_ddog_CommonStockCoveredUnderCappedCallsTransaction_4aea9f53-155b-4244-83c2-93a179a2e2dd" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_ddog_CostIncurredToPurchaseCappedCalls_75f5235f-62d9-4bed-8d7d-7761f3645e1a" xlink:href="ddog-20210630.xsd#ddog_CostIncurredToPurchaseCappedCalls"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_ded538fa-0783-41e9-acfd-4f21b01396dd" xlink:to="loc_ddog_CostIncurredToPurchaseCappedCalls_75f5235f-62d9-4bed-8d7d-7761f3645e1a" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_b005cd72-2f54-4017-a9fb-0069e7ea309a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_ded538fa-0783-41e9-acfd-4f21b01396dd" xlink:to="loc_us-gaap_DebtInstrumentTable_b005cd72-2f54-4017-a9fb-0069e7ea309a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_15f4ac02-1dc8-45d5-8e2b-b0f167d158bb" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_b005cd72-2f54-4017-a9fb-0069e7ea309a" xlink:to="loc_us-gaap_DebtInstrumentAxis_15f4ac02-1dc8-45d5-8e2b-b0f167d158bb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_15f4ac02-1dc8-45d5-8e2b-b0f167d158bb_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_15f4ac02-1dc8-45d5-8e2b-b0f167d158bb" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_15f4ac02-1dc8-45d5-8e2b-b0f167d158bb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_fa100369-1844-43a5-a386-510cbbd961ff" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_15f4ac02-1dc8-45d5-8e2b-b0f167d158bb" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_fa100369-1844-43a5-a386-510cbbd961ff" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ddog_A0125ConvertibleSeniorNotesDue2025Member_b4f270ec-2596-44d1-b7d1-cd17a0536cf0" xlink:href="ddog-20210630.xsd#ddog_A0125ConvertibleSeniorNotesDue2025Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_fa100369-1844-43a5-a386-510cbbd961ff" xlink:to="loc_ddog_A0125ConvertibleSeniorNotesDue2025Member_b4f270ec-2596-44d1-b7d1-cd17a0536cf0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_c31d124f-487d-4b4e-a567-88a696f144a4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_b005cd72-2f54-4017-a9fb-0069e7ea309a" xlink:to="loc_us-gaap_StatementClassOfStockAxis_c31d124f-487d-4b4e-a567-88a696f144a4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_c31d124f-487d-4b4e-a567-88a696f144a4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_c31d124f-487d-4b4e-a567-88a696f144a4" xlink:to="loc_us-gaap_ClassOfStockDomain_c31d124f-487d-4b4e-a567-88a696f144a4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_f70b461d-4185-44d1-a11f-42d5b602c4f6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_c31d124f-487d-4b4e-a567-88a696f144a4" xlink:to="loc_us-gaap_ClassOfStockDomain_f70b461d-4185-44d1-a11f-42d5b602c4f6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_064ba429-7ce8-41db-a898-8571caa001f2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_f70b461d-4185-44d1-a11f-42d5b602c4f6" xlink:to="loc_us-gaap_CommonClassAMember_064ba429-7ce8-41db-a898-8571caa001f2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_0ea7d25b-b715-4724-a347-d7f7d0201bfb" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_b005cd72-2f54-4017-a9fb-0069e7ea309a" xlink:to="loc_srt_RangeAxis_0ea7d25b-b715-4724-a347-d7f7d0201bfb" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_0ea7d25b-b715-4724-a347-d7f7d0201bfb_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_0ea7d25b-b715-4724-a347-d7f7d0201bfb" xlink:to="loc_srt_RangeMember_0ea7d25b-b715-4724-a347-d7f7d0201bfb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_1dabb2c5-d359-4d55-82bb-0400356bdcd0" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_0ea7d25b-b715-4724-a347-d7f7d0201bfb" xlink:to="loc_srt_RangeMember_1dabb2c5-d359-4d55-82bb-0400356bdcd0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_d0028d69-d1a7-45a7-a0d7-ed6566875016" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_1dabb2c5-d359-4d55-82bb-0400356bdcd0" xlink:to="loc_srt_MinimumMember_d0028d69-d1a7-45a7-a0d7-ed6566875016" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPeriodAxis_6ae86932-ed40-4d0e-95e7-ce9d16f807c4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentRedemptionPeriodAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_b005cd72-2f54-4017-a9fb-0069e7ea309a" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPeriodAxis_6ae86932-ed40-4d0e-95e7-ce9d16f807c4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_6ae86932-ed40-4d0e-95e7-ce9d16f807c4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentRedemptionPeriodDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentRedemptionPeriodAxis_6ae86932-ed40-4d0e-95e7-ce9d16f807c4" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_6ae86932-ed40-4d0e-95e7-ce9d16f807c4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_422ba1f6-2c1f-49d1-9f54-022139a9f263" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentRedemptionPeriodDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentRedemptionPeriodAxis_6ae86932-ed40-4d0e-95e7-ce9d16f807c4" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_422ba1f6-2c1f-49d1-9f54-022139a9f263" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPeriodOneMember_54b69fa6-72e5-43f7-b018-997109fb55f2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentRedemptionPeriodOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentRedemptionPeriodDomain_422ba1f6-2c1f-49d1-9f54-022139a9f263" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPeriodOneMember_54b69fa6-72e5-43f7-b018-997109fb55f2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ddog_DebtInstrumentConvertibleTermsAxis_923191f4-65bc-4ced-a326-84ecd1e88df2" xlink:href="ddog-20210630.xsd#ddog_DebtInstrumentConvertibleTermsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_b005cd72-2f54-4017-a9fb-0069e7ea309a" xlink:to="loc_ddog_DebtInstrumentConvertibleTermsAxis_923191f4-65bc-4ced-a326-84ecd1e88df2" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_ddog_DebtInstrumentConvertibleTermsDomain_923191f4-65bc-4ced-a326-84ecd1e88df2_default" xlink:href="ddog-20210630.xsd#ddog_DebtInstrumentConvertibleTermsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ddog_DebtInstrumentConvertibleTermsAxis_923191f4-65bc-4ced-a326-84ecd1e88df2" xlink:to="loc_ddog_DebtInstrumentConvertibleTermsDomain_923191f4-65bc-4ced-a326-84ecd1e88df2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ddog_DebtInstrumentConvertibleTermsDomain_56b17cc6-590b-4884-b40f-3623644d4947" xlink:href="ddog-20210630.xsd#ddog_DebtInstrumentConvertibleTermsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ddog_DebtInstrumentConvertibleTermsAxis_923191f4-65bc-4ced-a326-84ecd1e88df2" xlink:to="loc_ddog_DebtInstrumentConvertibleTermsDomain_56b17cc6-590b-4884-b40f-3623644d4947" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ddog_ScenarioOneMember_3ae234c7-9d95-48c6-86d8-b6bf347c9a29" xlink:href="ddog-20210630.xsd#ddog_ScenarioOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ddog_DebtInstrumentConvertibleTermsDomain_56b17cc6-590b-4884-b40f-3623644d4947" xlink:to="loc_ddog_ScenarioOneMember_3ae234c7-9d95-48c6-86d8-b6bf347c9a29" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ddog_ScenarioTwoMember_45fac737-fb62-4e01-ac15-423a54a52b62" xlink:href="ddog-20210630.xsd#ddog_ScenarioTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ddog_DebtInstrumentConvertibleTermsDomain_56b17cc6-590b-4884-b40f-3623644d4947" xlink:to="loc_ddog_ScenarioTwoMember_45fac737-fb62-4e01-ac15-423a54a52b62" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ddog_ScenarioThreeMember_bf11223e-b115-4b65-9a0b-5d7ca5ed3580" xlink:href="ddog-20210630.xsd#ddog_ScenarioThreeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ddog_DebtInstrumentConvertibleTermsDomain_56b17cc6-590b-4884-b40f-3623644d4947" xlink:to="loc_ddog_ScenarioThreeMember_bf11223e-b115-4b65-9a0b-5d7ca5ed3580" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CumulativeEffectPeriodOfAdoptionAxis_2f85bea2-138e-483d-8c70-06c44d7075d4" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_CumulativeEffectPeriodOfAdoptionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_b005cd72-2f54-4017-a9fb-0069e7ea309a" xlink:to="loc_srt_CumulativeEffectPeriodOfAdoptionAxis_2f85bea2-138e-483d-8c70-06c44d7075d4" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CumulativeEffectPeriodOfAdoptionDomain_2f85bea2-138e-483d-8c70-06c44d7075d4_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_CumulativeEffectPeriodOfAdoptionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CumulativeEffectPeriodOfAdoptionAxis_2f85bea2-138e-483d-8c70-06c44d7075d4" xlink:to="loc_srt_CumulativeEffectPeriodOfAdoptionDomain_2f85bea2-138e-483d-8c70-06c44d7075d4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CumulativeEffectPeriodOfAdoptionDomain_49d4c1d2-9571-435d-aa74-70f341c6f902" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_CumulativeEffectPeriodOfAdoptionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CumulativeEffectPeriodOfAdoptionAxis_2f85bea2-138e-483d-8c70-06c44d7075d4" xlink:to="loc_srt_CumulativeEffectPeriodOfAdoptionDomain_49d4c1d2-9571-435d-aa74-70f341c6f902" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CumulativeEffectPeriodOfAdoptionAdjustmentMember_459261b9-df0b-435f-a12b-c8ad7c36cde5" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_CumulativeEffectPeriodOfAdoptionAdjustmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_CumulativeEffectPeriodOfAdoptionDomain_49d4c1d2-9571-435d-aa74-70f341c6f902" xlink:to="loc_srt_CumulativeEffectPeriodOfAdoptionAdjustmentMember_459261b9-df0b-435f-a12b-c8ad7c36cde5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_0d5fde3f-31ab-4b97-a183-0c5b03b62dac" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AdjustmentsForNewAccountingPronouncementsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_b005cd72-2f54-4017-a9fb-0069e7ea309a" xlink:to="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_0d5fde3f-31ab-4b97-a183-0c5b03b62dac" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfAdoptionMember_0d5fde3f-31ab-4b97-a183-0c5b03b62dac_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TypeOfAdoptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_0d5fde3f-31ab-4b97-a183-0c5b03b62dac" xlink:to="loc_us-gaap_TypeOfAdoptionMember_0d5fde3f-31ab-4b97-a183-0c5b03b62dac_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfAdoptionMember_8f0f1840-f653-4056-a550-00893cd05397" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TypeOfAdoptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AdjustmentsForNewAccountingPronouncementsAxis_0d5fde3f-31ab-4b97-a183-0c5b03b62dac" xlink:to="loc_us-gaap_TypeOfAdoptionMember_8f0f1840-f653-4056-a550-00893cd05397" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountingStandardsUpdate202006Member_4a1eac80-fd07-484b-8a6f-1d527cf3eff8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AccountingStandardsUpdate202006Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfAdoptionMember_8f0f1840-f653-4056-a550-00893cd05397" xlink:to="loc_us-gaap_AccountingStandardsUpdate202006Member_4a1eac80-fd07-484b-8a6f-1d527cf3eff8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_66377b74-7ad7-47b6-ac40-a28b74e0a638" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_b005cd72-2f54-4017-a9fb-0069e7ea309a" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_66377b74-7ad7-47b6-ac40-a28b74e0a638" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_66377b74-7ad7-47b6-ac40-a28b74e0a638_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_66377b74-7ad7-47b6-ac40-a28b74e0a638" xlink:to="loc_us-gaap_EquityComponentDomain_66377b74-7ad7-47b6-ac40-a28b74e0a638_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_60bdffc5-0ff8-4e58-9b07-cfb3d5184c82" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_66377b74-7ad7-47b6-ac40-a28b74e0a638" xlink:to="loc_us-gaap_EquityComponentDomain_60bdffc5-0ff8-4e58-9b07-cfb3d5184c82" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_a1f755d9-bbb4-4857-9412-c9f0a88a84dc" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_60bdffc5-0ff8-4e58-9b07-cfb3d5184c82" xlink:to="loc_us-gaap_RetainedEarningsMember_a1f755d9-bbb4-4857-9412-c9f0a88a84dc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_e231752e-9bba-42d6-b624-8b963d482058" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_60bdffc5-0ff8-4e58-9b07-cfb3d5184c82" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_e231752e-9bba-42d6-b624-8b963d482058" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.datadoghq.com/role/ConvertibleSeniorNotesSummaryofNetCarryingAmountofLiabilityComponentof2025NotesDetails" xlink:type="simple" xlink:href="ddog-20210630.xsd#ConvertibleSeniorNotesSummaryofNetCarryingAmountofLiabilityComponentof2025NotesDetails"/>
  <link:definitionLink xlink:role="http://www.datadoghq.com/role/ConvertibleSeniorNotesSummaryofNetCarryingAmountofLiabilityComponentof2025NotesDetails" xlink:type="extended" id="i236de1ea8c544d94933d539c7bae5b9f_ConvertibleSeniorNotesSummaryofNetCarryingAmountofLiabilityComponentof2025NotesDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_185bace8-22a7-411b-b2a5-7eeda4ea2cc5" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_c0f2eac4-384b-4eec-98be-36239d4580e7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_185bace8-22a7-411b-b2a5-7eeda4ea2cc5" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_c0f2eac4-384b-4eec-98be-36239d4580e7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentUnamortizedDiscount_b59eaa2c-a224-4d53-9de2-c69cb39d6f4a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentUnamortizedDiscount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_185bace8-22a7-411b-b2a5-7eeda4ea2cc5" xlink:to="loc_us-gaap_DebtInstrumentUnamortizedDiscount_b59eaa2c-a224-4d53-9de2-c69cb39d6f4a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnamortizedDebtIssuanceExpense_32e8e2b8-2388-4234-9384-707b7becf9eb" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_UnamortizedDebtIssuanceExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_185bace8-22a7-411b-b2a5-7eeda4ea2cc5" xlink:to="loc_us-gaap_UnamortizedDebtIssuanceExpense_32e8e2b8-2388-4234-9384-707b7becf9eb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleLongTermNotesPayable_2cecbd3d-e029-4a72-9bf3-41a9744954d7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConvertibleLongTermNotesPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_185bace8-22a7-411b-b2a5-7eeda4ea2cc5" xlink:to="loc_us-gaap_ConvertibleLongTermNotesPayable_2cecbd3d-e029-4a72-9bf3-41a9744954d7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleCarryingAmountOfTheEquityComponent_ccf6bb49-07d8-42a9-a184-8a0517b716bf" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentConvertibleCarryingAmountOfTheEquityComponent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_185bace8-22a7-411b-b2a5-7eeda4ea2cc5" xlink:to="loc_us-gaap_DebtInstrumentConvertibleCarryingAmountOfTheEquityComponent_ccf6bb49-07d8-42a9-a184-8a0517b716bf" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_2880e84d-1b84-49a4-a927-1aec0d29f639" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_185bace8-22a7-411b-b2a5-7eeda4ea2cc5" xlink:to="loc_us-gaap_DebtInstrumentTable_2880e84d-1b84-49a4-a927-1aec0d29f639" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_c429868e-5688-44e1-b38b-f8bbfa9671b0" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_2880e84d-1b84-49a4-a927-1aec0d29f639" xlink:to="loc_us-gaap_DebtInstrumentAxis_c429868e-5688-44e1-b38b-f8bbfa9671b0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_c429868e-5688-44e1-b38b-f8bbfa9671b0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_c429868e-5688-44e1-b38b-f8bbfa9671b0" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_c429868e-5688-44e1-b38b-f8bbfa9671b0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_4453a3e2-0ca6-4aa9-aef6-3f1275625047" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_c429868e-5688-44e1-b38b-f8bbfa9671b0" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_4453a3e2-0ca6-4aa9-aef6-3f1275625047" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ddog_A0125ConvertibleSeniorNotesDue2025Member_b720c66b-f6db-41f7-8262-f889aa2f47e9" xlink:href="ddog-20210630.xsd#ddog_A0125ConvertibleSeniorNotesDue2025Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_4453a3e2-0ca6-4aa9-aef6-3f1275625047" xlink:to="loc_ddog_A0125ConvertibleSeniorNotesDue2025Member_b720c66b-f6db-41f7-8262-f889aa2f47e9" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.datadoghq.com/role/ConvertibleSeniorNotesInterestExpenserelatedto2025NotesDetails" xlink:type="simple" xlink:href="ddog-20210630.xsd#ConvertibleSeniorNotesInterestExpenserelatedto2025NotesDetails"/>
  <link:definitionLink xlink:role="http://www.datadoghq.com/role/ConvertibleSeniorNotesInterestExpenserelatedto2025NotesDetails" xlink:type="extended" id="i22a2213e054e43c3a46599187336b21c_ConvertibleSeniorNotesInterestExpenserelatedto2025NotesDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_26a593a4-2d8b-4d62-8ece-1525d5137af9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseDebtExcludingAmortization_e970f8ef-b154-4581-ae22-5f4443f109e1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_InterestExpenseDebtExcludingAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_26a593a4-2d8b-4d62-8ece-1525d5137af9" xlink:to="loc_us-gaap_InterestExpenseDebtExcludingAmortization_e970f8ef-b154-4581-ae22-5f4443f109e1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfDebtDiscountPremium_1cbbf512-1043-46a6-ba3e-3dddf29037b0" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AmortizationOfDebtDiscountPremium"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_26a593a4-2d8b-4d62-8ece-1525d5137af9" xlink:to="loc_us-gaap_AmortizationOfDebtDiscountPremium_1cbbf512-1043-46a6-ba3e-3dddf29037b0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfFinancingCosts_e8214998-13f1-4ccc-a08f-2342c7d8842f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AmortizationOfFinancingCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_26a593a4-2d8b-4d62-8ece-1525d5137af9" xlink:to="loc_us-gaap_AmortizationOfFinancingCosts_e8214998-13f1-4ccc-a08f-2342c7d8842f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseDebt_7df70781-c5f2-46ce-8216-9b50f6b8b18d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_InterestExpenseDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_26a593a4-2d8b-4d62-8ece-1525d5137af9" xlink:to="loc_us-gaap_InterestExpenseDebt_7df70781-c5f2-46ce-8216-9b50f6b8b18d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_bf4139d0-11d7-401c-bf0f-136f770acd4c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_26a593a4-2d8b-4d62-8ece-1525d5137af9" xlink:to="loc_us-gaap_DebtInstrumentTable_bf4139d0-11d7-401c-bf0f-136f770acd4c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_381f1ee6-a982-49c8-a06c-c25c7952768d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_bf4139d0-11d7-401c-bf0f-136f770acd4c" xlink:to="loc_us-gaap_DebtInstrumentAxis_381f1ee6-a982-49c8-a06c-c25c7952768d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_381f1ee6-a982-49c8-a06c-c25c7952768d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_381f1ee6-a982-49c8-a06c-c25c7952768d" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_381f1ee6-a982-49c8-a06c-c25c7952768d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_6aeb8c9f-9a26-4696-98a3-a1cb59002ed6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_381f1ee6-a982-49c8-a06c-c25c7952768d" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_6aeb8c9f-9a26-4696-98a3-a1cb59002ed6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ddog_A0125ConvertibleSeniorNotesDue2025Member_43cdcbda-6379-4b0b-8546-4e47f92109c6" xlink:href="ddog-20210630.xsd#ddog_A0125ConvertibleSeniorNotesDue2025Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_6aeb8c9f-9a26-4696-98a3-a1cb59002ed6" xlink:to="loc_ddog_A0125ConvertibleSeniorNotesDue2025Member_43cdcbda-6379-4b0b-8546-4e47f92109c6" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.datadoghq.com/role/RevenueScheduleofRevenuebyGeographicAreaDetails" xlink:type="simple" xlink:href="ddog-20210630.xsd#RevenueScheduleofRevenuebyGeographicAreaDetails"/>
  <link:definitionLink xlink:role="http://www.datadoghq.com/role/RevenueScheduleofRevenuebyGeographicAreaDetails" xlink:type="extended" id="i997d11a8940740349c66c735038a2ed1_RevenueScheduleofRevenuebyGeographicAreaDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_def7e145-e632-44eb-ac0f-ec3b572abc25" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_a3a5e0dc-37a2-40c3-8ef5-b31aa2cfec28" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_def7e145-e632-44eb-ac0f-ec3b572abc25" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_a3a5e0dc-37a2-40c3-8ef5-b31aa2cfec28" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_d1b0e177-6a06-4227-bf54-6e3d5ed365b4" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_def7e145-e632-44eb-ac0f-ec3b572abc25" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_d1b0e177-6a06-4227-bf54-6e3d5ed365b4" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_59330697-3396-4be9-9f89-f01c410ff25f" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_d1b0e177-6a06-4227-bf54-6e3d5ed365b4" xlink:to="loc_srt_StatementGeographicalAxis_59330697-3396-4be9-9f89-f01c410ff25f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_59330697-3396-4be9-9f89-f01c410ff25f_default" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_59330697-3396-4be9-9f89-f01c410ff25f" xlink:to="loc_srt_SegmentGeographicalDomain_59330697-3396-4be9-9f89-f01c410ff25f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_d17e9a98-065e-4a0b-b0eb-b686431266f9" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_59330697-3396-4be9-9f89-f01c410ff25f" xlink:to="loc_srt_SegmentGeographicalDomain_d17e9a98-065e-4a0b-b0eb-b686431266f9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NorthAmericaMember_07f670a6-2447-49bf-84c1-672794e53afd" xlink:href="https://xbrl.fasb.org/srt/2021/elts/srt-2021-01-31.xsd#srt_NorthAmericaMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_d17e9a98-065e-4a0b-b0eb-b686431266f9" xlink:to="loc_srt_NorthAmericaMember_07f670a6-2447-49bf-84c1-672794e53afd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ddog_InternationalMember_e02f7322-005e-4d34-823d-faed9b44c6ea" xlink:href="ddog-20210630.xsd#ddog_InternationalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_d17e9a98-065e-4a0b-b0eb-b686431266f9" xlink:to="loc_ddog_InternationalMember_e02f7322-005e-4d34-823d-faed9b44c6ea" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.datadoghq.com/role/RevenueAdditionalInformationDetails" xlink:type="simple" xlink:href="ddog-20210630.xsd#RevenueAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://www.datadoghq.com/role/RevenueAdditionalInformationDetails" xlink:type="extended" id="id2fd6346e5af41f9a5da399651c3c49a_RevenueAdditionalInformationDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_86b11735-063f-4d37-9222-64f5d3af8762" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligation_ff2e0ccc-617c-4253-905e-e7bc695a63d3" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_86b11735-063f-4d37-9222-64f5d3af8762" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligation_ff2e0ccc-617c-4253-905e-e7bc695a63d3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_9b8ab148-f378-47fb-aceb-733db19be3fc" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_86b11735-063f-4d37-9222-64f5d3af8762" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_9b8ab148-f378-47fb-aceb-733db19be3fc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_b3b8eb0a-2243-4493-b539-2a2151ea4110" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_86b11735-063f-4d37-9222-64f5d3af8762" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_b3b8eb0a-2243-4493-b539-2a2151ea4110" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_2728fac4-f72b-4558-b630-8b55aee882d8" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_b3b8eb0a-2243-4493-b539-2a2151ea4110" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_2728fac4-f72b-4558-b630-8b55aee882d8" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.datadoghq.com/role/RevenueAdditionalInformationDetails_1" xlink:type="simple" xlink:href="ddog-20210630.xsd#RevenueAdditionalInformationDetails_1"/>
  <link:definitionLink xlink:role="http://www.datadoghq.com/role/RevenueAdditionalInformationDetails_1" xlink:type="extended" id="i8a099e52a9de4086b25a2acd49e8336a_RevenueAdditionalInformationDetails_1">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_86b11735-063f-4d37-9222-64f5d3af8762" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligation_ff2e0ccc-617c-4253-905e-e7bc695a63d3" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_86b11735-063f-4d37-9222-64f5d3af8762" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligation_ff2e0ccc-617c-4253-905e-e7bc695a63d3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_9b8ab148-f378-47fb-aceb-733db19be3fc" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_86b11735-063f-4d37-9222-64f5d3af8762" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_9b8ab148-f378-47fb-aceb-733db19be3fc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_b3b8eb0a-2243-4493-b539-2a2151ea4110" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionLineItems_86b11735-063f-4d37-9222-64f5d3af8762" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionTable_b3b8eb0a-2243-4493-b539-2a2151ea4110" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.datadoghq.com/role/StockholdersEquityAdditionalInformationDetails" xlink:type="simple" xlink:href="ddog-20210630.xsd#StockholdersEquityAdditionalInformationDetails"/>
  <link:definitionLink xlink:role="http://www.datadoghq.com/role/StockholdersEquityAdditionalInformationDetails" xlink:type="extended" id="i362e91b8b43146e2a817bab99a59fd84_StockholdersEquityAdditionalInformationDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_c0a765ad-30bb-4985-954e-fd2de00473c1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_ddog_NumberOfCommonStockClasses_575c57b1-c48a-4ff3-b75e-0a54da58d331" xlink:href="ddog-20210630.xsd#ddog_NumberOfCommonStockClasses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_c0a765ad-30bb-4985-954e-fd2de00473c1" xlink:to="loc_ddog_NumberOfCommonStockClasses_575c57b1-c48a-4ff3-b75e-0a54da58d331" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ddog_CommonStockVotingRightsNumberOfVotePerShare_f3c3687a-d047-40d8-a43c-9414b60677ee" xlink:href="ddog-20210630.xsd#ddog_CommonStockVotingRightsNumberOfVotePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_c0a765ad-30bb-4985-954e-fd2de00473c1" xlink:to="loc_ddog_CommonStockVotingRightsNumberOfVotePerShare_f3c3687a-d047-40d8-a43c-9414b60677ee" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConversionOfStockSharesConverted1_6565ab9f-7fca-4eff-8deb-d27bfa90bdc9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ConversionOfStockSharesConverted1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_c0a765ad-30bb-4985-954e-fd2de00473c1" xlink:to="loc_us-gaap_ConversionOfStockSharesConverted1_6565ab9f-7fca-4eff-8deb-d27bfa90bdc9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_2e4afa59-4589-4c4f-ac95-73de74cf5ee7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_c0a765ad-30bb-4985-954e-fd2de00473c1" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_2e4afa59-4589-4c4f-ac95-73de74cf5ee7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_00f3d972-addf-438c-9bc5-6a56b7dc9657" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_c0a765ad-30bb-4985-954e-fd2de00473c1" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_00f3d972-addf-438c-9bc5-6a56b7dc9657" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_63836078-ffaf-4147-8849-9d13e959c26e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_c0a765ad-30bb-4985-954e-fd2de00473c1" xlink:to="loc_us-gaap_CommonStockSharesIssued_63836078-ffaf-4147-8849-9d13e959c26e" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_ddog_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfEquityIncentivePlan_e39ec9bd-0bb9-4080-af3b-a81bdf3502a0" xlink:href="ddog-20210630.xsd#ddog_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfEquityIncentivePlan"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_c0a765ad-30bb-4985-954e-fd2de00473c1" xlink:to="loc_ddog_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfEquityIncentivePlan_e39ec9bd-0bb9-4080-af3b-a81bdf3502a0" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_1933843b-fc4c-4338-81ca-3ef657eef9e5" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_c0a765ad-30bb-4985-954e-fd2de00473c1" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_1933843b-fc4c-4338-81ca-3ef657eef9e5" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_21220202-ee23-44d6-b97a-90fa0cbbc99a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_c0a765ad-30bb-4985-954e-fd2de00473c1" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_21220202-ee23-44d6-b97a-90fa0cbbc99a" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions_6ceefd76-70ba-4831-8b51-ad83855f3cfe" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_c0a765ad-30bb-4985-954e-fd2de00473c1" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions_6ceefd76-70ba-4831-8b51-ad83855f3cfe" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_1eeeed68-002b-478b-9eb1-a4dfdce41225" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_c0a765ad-30bb-4985-954e-fd2de00473c1" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_1eeeed68-002b-478b-9eb1-a4dfdce41225" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_36a8970e-5040-409f-a72a-ccb0a2c93b58" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_c0a765ad-30bb-4985-954e-fd2de00473c1" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_36a8970e-5040-409f-a72a-ccb0a2c93b58" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_2e694c15-1b76-46e8-a660-691dd7f8412e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_c0a765ad-30bb-4985-954e-fd2de00473c1" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_2e694c15-1b76-46e8-a660-691dd7f8412e" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromStockOptionsExercised_48531c29-36f1-401d-ad4e-5fc84aba7c62" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ProceedsFromStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_c0a765ad-30bb-4985-954e-fd2de00473c1" xlink:to="loc_us-gaap_ProceedsFromStockOptionsExercised_48531c29-36f1-401d-ad4e-5fc84aba7c62" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue_323e6527-a13f-4a98-99d1-248d3be5d19b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_c0a765ad-30bb-4985-954e-fd2de00473c1" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue_323e6527-a13f-4a98-99d1-248d3be5d19b" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_6b2eb6e9-4b97-41b7-a329-1c058e3fcd6f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_c0a765ad-30bb-4985-954e-fd2de00473c1" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_6b2eb6e9-4b97-41b7-a329-1c058e3fcd6f" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedInPeriodFairValue1_ceed03fe-c218-4844-bce5-f322df5f4d02" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedInPeriodFairValue1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_c0a765ad-30bb-4985-954e-fd2de00473c1" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedInPeriodFairValue1_ceed03fe-c218-4844-bce5-f322df5f4d02" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_ddog_CommonStockIssuedSubjectToRepurchaseRelatedToEarlyExerciseOfOptions_de59c11f-1694-41d5-bfa8-d22768a332b8" xlink:href="ddog-20210630.xsd#ddog_CommonStockIssuedSubjectToRepurchaseRelatedToEarlyExerciseOfOptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_c0a765ad-30bb-4985-954e-fd2de00473c1" xlink:to="loc_ddog_CommonStockIssuedSubjectToRepurchaseRelatedToEarlyExerciseOfOptions_de59c11f-1694-41d5-bfa8-d22768a332b8" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_f38d8167-00c1-437e-931f-20e734566f70" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_c0a765ad-30bb-4985-954e-fd2de00473c1" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_f38d8167-00c1-437e-931f-20e734566f70" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_e62947fb-3b3e-46b1-a9d3-dfaf8a2639d9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_c0a765ad-30bb-4985-954e-fd2de00473c1" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_e62947fb-3b3e-46b1-a9d3-dfaf8a2639d9" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions_8229f446-6a2e-40c4-9c22-6a522457e375" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_c0a765ad-30bb-4985-954e-fd2de00473c1" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions_8229f446-6a2e-40c4-9c22-6a522457e375" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_44e07fa2-f3b4-458d-91b7-1f3298f33f35" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod_a2dd8707-bedd-4fd7-ad44-abb6f221a0d9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_c0a765ad-30bb-4985-954e-fd2de00473c1" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod_a2dd8707-bedd-4fd7-ad44-abb6f221a0d9" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_ddog_EmployeeStockPurchasePlansPurchasePricePercentage_68c169a1-2f20-4747-b84d-d05e08908dbc" xlink:href="ddog-20210630.xsd#ddog_EmployeeStockPurchasePlansPurchasePricePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_c0a765ad-30bb-4985-954e-fd2de00473c1" xlink:to="loc_ddog_EmployeeStockPurchasePlansPurchasePricePercentage_68c169a1-2f20-4747-b84d-d05e08908dbc" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_367de344-07a3-425e-a033-3f940169109b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_c0a765ad-30bb-4985-954e-fd2de00473c1" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_367de344-07a3-425e-a033-3f940169109b" xlink:type="arc" order="24"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsRelatedToTaxWithholdingForShareBasedCompensation_1174fe8f-307d-421b-8f42-23c78c200c30" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PaymentsRelatedToTaxWithholdingForShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_c0a765ad-30bb-4985-954e-fd2de00473c1" xlink:to="loc_us-gaap_PaymentsRelatedToTaxWithholdingForShareBasedCompensation_1174fe8f-307d-421b-8f42-23c78c200c30" xlink:type="arc" order="25"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_9ea95164-004f-4dad-ae03-da84292f8a61" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_c0a765ad-30bb-4985-954e-fd2de00473c1" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_9ea95164-004f-4dad-ae03-da84292f8a61" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_95529bbb-f992-44f0-90c7-be3a76ae1452" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_9ea95164-004f-4dad-ae03-da84292f8a61" xlink:to="loc_us-gaap_StatementClassOfStockAxis_95529bbb-f992-44f0-90c7-be3a76ae1452" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_95529bbb-f992-44f0-90c7-be3a76ae1452_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_95529bbb-f992-44f0-90c7-be3a76ae1452" xlink:to="loc_us-gaap_ClassOfStockDomain_95529bbb-f992-44f0-90c7-be3a76ae1452_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_bc151b10-ac20-4ce7-a352-a54c5ab10dcd" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_95529bbb-f992-44f0-90c7-be3a76ae1452" xlink:to="loc_us-gaap_ClassOfStockDomain_bc151b10-ac20-4ce7-a352-a54c5ab10dcd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_9770488b-609c-4d78-86d6-a9c340f469de" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_bc151b10-ac20-4ce7-a352-a54c5ab10dcd" xlink:to="loc_us-gaap_CommonClassBMember_9770488b-609c-4d78-86d6-a9c340f469de" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_67b85c83-7311-4c21-b4d5-356afc766d0e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_bc151b10-ac20-4ce7-a352-a54c5ab10dcd" xlink:to="loc_us-gaap_CommonClassAMember_67b85c83-7311-4c21-b4d5-356afc766d0e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_c8bbc088-e115-4a68-9407-92ea70127e75" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_9ea95164-004f-4dad-ae03-da84292f8a61" xlink:to="loc_us-gaap_PlanNameAxis_c8bbc088-e115-4a68-9407-92ea70127e75" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_c8bbc088-e115-4a68-9407-92ea70127e75_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_c8bbc088-e115-4a68-9407-92ea70127e75" xlink:to="loc_us-gaap_PlanNameDomain_c8bbc088-e115-4a68-9407-92ea70127e75_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_7892306e-4d43-436c-b8f9-5fe211800e81" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_c8bbc088-e115-4a68-9407-92ea70127e75" xlink:to="loc_us-gaap_PlanNameDomain_7892306e-4d43-436c-b8f9-5fe211800e81" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ddog_TwoThousandNineteenEquityIncentivePlanMember_526227e4-110b-4142-9270-e42b00359d0e" xlink:href="ddog-20210630.xsd#ddog_TwoThousandNineteenEquityIncentivePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_7892306e-4d43-436c-b8f9-5fe211800e81" xlink:to="loc_ddog_TwoThousandNineteenEquityIncentivePlanMember_526227e4-110b-4142-9270-e42b00359d0e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ddog_EmployeeStockPurchasePlanMember_7d387d5d-3b9c-424e-ab98-6bf0ea8ccdb4" xlink:href="ddog-20210630.xsd#ddog_EmployeeStockPurchasePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_7892306e-4d43-436c-b8f9-5fe211800e81" xlink:to="loc_ddog_EmployeeStockPurchasePlanMember_7d387d5d-3b9c-424e-ab98-6bf0ea8ccdb4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_db7696ac-cf71-4d08-864c-62ec216cc689" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_9ea95164-004f-4dad-ae03-da84292f8a61" xlink:to="loc_us-gaap_AwardTypeAxis_db7696ac-cf71-4d08-864c-62ec216cc689" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_db7696ac-cf71-4d08-864c-62ec216cc689_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_db7696ac-cf71-4d08-864c-62ec216cc689" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_db7696ac-cf71-4d08-864c-62ec216cc689_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_403f58ec-a0d7-48c5-a20e-a8423e19a562" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_db7696ac-cf71-4d08-864c-62ec216cc689" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_403f58ec-a0d7-48c5-a20e-a8423e19a562" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_a348d5bc-54dc-4e1f-8d9f-513efdbac565" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_403f58ec-a0d7-48c5-a20e-a8423e19a562" xlink:to="loc_us-gaap_EmployeeStockOptionMember_a348d5bc-54dc-4e1f-8d9f-513efdbac565" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_1343d873-ad1b-4192-8517-9503b1a36b5f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_PerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_403f58ec-a0d7-48c5-a20e-a8423e19a562" xlink:to="loc_us-gaap_PerformanceSharesMember_1343d873-ad1b-4192-8517-9503b1a36b5f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_672dbc2d-8a44-45e0-958f-b29accdbcced" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_403f58ec-a0d7-48c5-a20e-a8423e19a562" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_672dbc2d-8a44-45e0-958f-b29accdbcced" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.datadoghq.com/role/StockholdersEquitySummaryofActivityforUnvestedRSUsDetails" xlink:type="simple" xlink:href="ddog-20210630.xsd#StockholdersEquitySummaryofActivityforUnvestedRSUsDetails"/>
  <link:definitionLink xlink:role="http://www.datadoghq.com/role/StockholdersEquitySummaryofActivityforUnvestedRSUsDetails" xlink:type="extended" id="ic609e915ca1f4dbbb0b5ae27afc6454a_StockholdersEquitySummaryofActivityforUnvestedRSUsDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_835d3b0a-48d1-4187-8bec-87472a2e1f77" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_70699540-d4cd-4320-8277-d9a2b90d745a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_835d3b0a-48d1-4187-8bec-87472a2e1f77" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_70699540-d4cd-4320-8277-d9a2b90d745a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_6ce9eff5-006b-4395-86b7-8253dd7a587b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_70699540-d4cd-4320-8277-d9a2b90d745a" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_6ce9eff5-006b-4395-86b7-8253dd7a587b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_6cf89786-60d2-43f4-9ae3-01e751733110" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_70699540-d4cd-4320-8277-d9a2b90d745a" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_6cf89786-60d2-43f4-9ae3-01e751733110" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_72a98d0d-ea54-405f-be8e-e3e9c0836612" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_70699540-d4cd-4320-8277-d9a2b90d745a" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_72a98d0d-ea54-405f-be8e-e3e9c0836612" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_4473dd40-57b6-4c9f-9a1a-53dcae9d767a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_70699540-d4cd-4320-8277-d9a2b90d745a" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_4473dd40-57b6-4c9f-9a1a-53dcae9d767a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_5d37d719-6cc9-4ede-b10e-728a2712ae20" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_4ced0063-3153-4b65-8ab9-52aaa23c9647" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_835d3b0a-48d1-4187-8bec-87472a2e1f77" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_4ced0063-3153-4b65-8ab9-52aaa23c9647" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_e7c7832a-4f66-4664-a4c0-2bb1be927c2a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_4ced0063-3153-4b65-8ab9-52aaa23c9647" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_e7c7832a-4f66-4664-a4c0-2bb1be927c2a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_0b957652-e480-4fb0-a21f-cb7aa546a043" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_4ced0063-3153-4b65-8ab9-52aaa23c9647" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_0b957652-e480-4fb0-a21f-cb7aa546a043" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_453beaec-d45f-4546-8dd6-5a87b15beea6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_4ced0063-3153-4b65-8ab9-52aaa23c9647" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_453beaec-d45f-4546-8dd6-5a87b15beea6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_b809dfc7-d9f6-4c7d-a6c6-630834891ec5" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_4ced0063-3153-4b65-8ab9-52aaa23c9647" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_b809dfc7-d9f6-4c7d-a6c6-630834891ec5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_421b1f65-2237-4570-a145-0108cbfe6d44" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_34b7fa18-0813-472c-9f58-401f7c9e5302" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_835d3b0a-48d1-4187-8bec-87472a2e1f77" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_34b7fa18-0813-472c-9f58-401f7c9e5302" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_a0782c82-3285-4a71-941c-9706d5b45894" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_34b7fa18-0813-472c-9f58-401f7c9e5302" xlink:to="loc_us-gaap_AwardTypeAxis_a0782c82-3285-4a71-941c-9706d5b45894" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_a0782c82-3285-4a71-941c-9706d5b45894_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_a0782c82-3285-4a71-941c-9706d5b45894" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_a0782c82-3285-4a71-941c-9706d5b45894_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_f940c7df-3eee-4134-b740-6aa4fab70073" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_a0782c82-3285-4a71-941c-9706d5b45894" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_f940c7df-3eee-4134-b740-6aa4fab70073" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_942e23eb-5aec-4381-937d-b2a87d95710b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_f940c7df-3eee-4134-b740-6aa4fab70073" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_942e23eb-5aec-4381-937d-b2a87d95710b" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.datadoghq.com/role/StockholdersEquitySummaryofStockbasedCompensationExpenseDetails" xlink:type="simple" xlink:href="ddog-20210630.xsd#StockholdersEquitySummaryofStockbasedCompensationExpenseDetails"/>
  <link:definitionLink xlink:role="http://www.datadoghq.com/role/StockholdersEquitySummaryofStockbasedCompensationExpenseDetails" xlink:type="extended" id="iac4f3d1e9e3c4bd0bbecbc2816dcbfdb_StockholdersEquitySummaryofStockbasedCompensationExpenseDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_c6f1937c-56ba-4799-9cc3-723d53c6cefb" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_376232da-7488-424f-8b69-30e98bed4f2d" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_c6f1937c-56ba-4799-9cc3-723d53c6cefb" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_376232da-7488-424f-8b69-30e98bed4f2d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsCapitalizedAmount_251b9ac8-2e2e-414f-9f09-6e92dcde11b0" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsCapitalizedAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_c6f1937c-56ba-4799-9cc3-723d53c6cefb" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsCapitalizedAmount_251b9ac8-2e2e-414f-9f09-6e92dcde11b0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardCompensationCost1_5dc6d9e3-fc65-4ad2-a279-787460ba64ab" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardCompensationCost1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_c6f1937c-56ba-4799-9cc3-723d53c6cefb" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardCompensationCost1_5dc6d9e3-fc65-4ad2-a279-787460ba64ab" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_11c8d881-21e3-4c2f-8a5b-f99b13e5728f" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_c6f1937c-56ba-4799-9cc3-723d53c6cefb" xlink:to="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_11c8d881-21e3-4c2f-8a5b-f99b13e5728f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_0d881e23-3411-4415-b562-cb1f1622dc95" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncomeStatementLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_11c8d881-21e3-4c2f-8a5b-f99b13e5728f" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_0d881e23-3411-4415-b562-cb1f1622dc95" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_0d881e23-3411-4415-b562-cb1f1622dc95_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_0d881e23-3411-4415-b562-cb1f1622dc95" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_0d881e23-3411-4415-b562-cb1f1622dc95_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_80c19fac-54b7-441a-a0a1-be315bdb0078" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_0d881e23-3411-4415-b562-cb1f1622dc95" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_80c19fac-54b7-441a-a0a1-be315bdb0078" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfSalesMember_cdeb283d-0ead-4b97-aaa8-79be1652e9d1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CostOfSalesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_80c19fac-54b7-441a-a0a1-be315bdb0078" xlink:to="loc_us-gaap_CostOfSalesMember_cdeb283d-0ead-4b97-aaa8-79be1652e9d1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpenseMember_cd500756-5380-4abf-9454-62f935d5aa69" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ResearchAndDevelopmentExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_80c19fac-54b7-441a-a0a1-be315bdb0078" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpenseMember_cd500756-5380-4abf-9454-62f935d5aa69" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingAndMarketingExpenseMember_64041a17-a273-449e-a0d3-177d0aff9f38" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_SellingAndMarketingExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_80c19fac-54b7-441a-a0a1-be315bdb0078" xlink:to="loc_us-gaap_SellingAndMarketingExpenseMember_64041a17-a273-449e-a0d3-177d0aff9f38" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpenseMember_75e009a7-28be-499c-9436-7539a45151b6" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_GeneralAndAdministrativeExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_80c19fac-54b7-441a-a0a1-be315bdb0078" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpenseMember_75e009a7-28be-499c-9436-7539a45151b6" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.datadoghq.com/role/NetLossIncomePerShareScheduleofCalculationofBasicandDilutedNetLossPerShareDetails" xlink:type="simple" xlink:href="ddog-20210630.xsd#NetLossIncomePerShareScheduleofCalculationofBasicandDilutedNetLossPerShareDetails"/>
  <link:definitionLink xlink:role="http://www.datadoghq.com/role/NetLossIncomePerShareScheduleofCalculationofBasicandDilutedNetLossPerShareDetails" xlink:type="extended" id="i78352cd49b924003bef5f82c069cb300_NetLossIncomePerShareScheduleofCalculationofBasicandDilutedNetLossPerShareDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareBasicLineItems_bac46014-a441-481f-a6ed-34aa9bdbccc1" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EarningsPerShareBasicLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareBasicAbstract_a4afba95-cd38-4726-89ec-673f0c9d9881" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EarningsPerShareBasicAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicLineItems_bac46014-a441-481f-a6ed-34aa9bdbccc1" xlink:to="loc_us-gaap_EarningsPerShareBasicAbstract_a4afba95-cd38-4726-89ec-673f0c9d9881" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_160b4c9f-a207-4149-adea-155d869b79bd" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicAbstract_a4afba95-cd38-4726-89ec-673f0c9d9881" xlink:to="loc_us-gaap_NetIncomeLoss_160b4c9f-a207-4149-adea-155d869b79bd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_d637aff7-b16a-41dc-a057-36b2d37a4f6c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicAbstract_a4afba95-cd38-4726-89ec-673f0c9d9881" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_d637aff7-b16a-41dc-a057-36b2d37a4f6c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareBasic_ef29529d-73ea-427f-8638-aabf2316fb18" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EarningsPerShareBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicAbstract_a4afba95-cd38-4726-89ec-673f0c9d9881" xlink:to="loc_us-gaap_EarningsPerShareBasic_ef29529d-73ea-427f-8638-aabf2316fb18" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareDilutedAbstract_dd88ca2f-0c67-4026-b016-564f35b3b483" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EarningsPerShareDilutedAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicLineItems_bac46014-a441-481f-a6ed-34aa9bdbccc1" xlink:to="loc_us-gaap_EarningsPerShareDilutedAbstract_dd88ca2f-0c67-4026-b016-564f35b3b483" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_fe088941-c2b5-4466-bf95-a7647efa84a3" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_NetIncomeLoss"/>
    <link:loc xlink:type="locator" xlink:label="loc_ddog_ReallocationOfUndistributedIncomeLossResultOfConversionOfCommonStock_338a9777-e43b-4fc0-8533-3d9caf7a88af" xlink:href="ddog-20210630.xsd#ddog_ReallocationOfUndistributedIncomeLossResultOfConversionOfCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareDilutedAbstract_dd88ca2f-0c67-4026-b016-564f35b3b483" xlink:to="loc_ddog_ReallocationOfUndistributedIncomeLossResultOfConversionOfCommonStock_338a9777-e43b-4fc0-8533-3d9caf7a88af" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UndistributedEarningsLossAvailableToCommonShareholdersDiluted_8f6ca9b5-19d0-4fc8-b73e-5870f79c8050" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_UndistributedEarningsLossAvailableToCommonShareholdersDiluted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareDilutedAbstract_dd88ca2f-0c67-4026-b016-564f35b3b483" xlink:to="loc_us-gaap_UndistributedEarningsLossAvailableToCommonShareholdersDiluted_8f6ca9b5-19d0-4fc8-b73e-5870f79c8050" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_992f935b-fb8f-4f36-a50b-d5b260a8ac55" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustmentAbstract_06832b7d-5dc5-45a2-b3a4-4feed46b6914" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustmentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicLineItems_bac46014-a441-481f-a6ed-34aa9bdbccc1" xlink:to="loc_us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustmentAbstract_06832b7d-5dc5-45a2-b3a4-4feed46b6914" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ddog_WeightedAverageNumberDilutedSharesOutstandingConversionOfCommonSharesClass_99aa6519-9b0e-46ca-848c-308835b2876b" xlink:href="ddog-20210630.xsd#ddog_WeightedAverageNumberDilutedSharesOutstandingConversionOfCommonSharesClass"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustmentAbstract_06832b7d-5dc5-45a2-b3a4-4feed46b6914" xlink:to="loc_ddog_WeightedAverageNumberDilutedSharesOutstandingConversionOfCommonSharesClass_99aa6519-9b0e-46ca-848c-308835b2876b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements_a4d544ff-3b41-425d-a219-33806cc6847b" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustmentAbstract_06832b7d-5dc5-45a2-b3a4-4feed46b6914" xlink:to="loc_us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements_a4d544ff-3b41-425d-a219-33806cc6847b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_1627e4bc-c3c1-49fb-85d0-390993aa306e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicLineItems_bac46014-a441-481f-a6ed-34aa9bdbccc1" xlink:to="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_1627e4bc-c3c1-49fb-85d0-390993aa306e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareDiluted_a682f2c3-8bd3-4651-8844-c1be624a3aca" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EarningsPerShareDiluted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicLineItems_bac46014-a441-481f-a6ed-34aa9bdbccc1" xlink:to="loc_us-gaap_EarningsPerShareDiluted_a682f2c3-8bd3-4651-8844-c1be624a3aca" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEarningsPerShareBasicByCommonClassTable_ef8ca422-27d7-4149-a410-0a71d2eb775c" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfEarningsPerShareBasicByCommonClassTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EarningsPerShareBasicLineItems_bac46014-a441-481f-a6ed-34aa9bdbccc1" xlink:to="loc_us-gaap_ScheduleOfEarningsPerShareBasicByCommonClassTable_ef8ca422-27d7-4149-a410-0a71d2eb775c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_7b90986a-6fa8-4cd8-b7b2-5f4907c846ea" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEarningsPerShareBasicByCommonClassTable_ef8ca422-27d7-4149-a410-0a71d2eb775c" xlink:to="loc_us-gaap_StatementClassOfStockAxis_7b90986a-6fa8-4cd8-b7b2-5f4907c846ea" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_7b90986a-6fa8-4cd8-b7b2-5f4907c846ea_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_7b90986a-6fa8-4cd8-b7b2-5f4907c846ea" xlink:to="loc_us-gaap_ClassOfStockDomain_7b90986a-6fa8-4cd8-b7b2-5f4907c846ea_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_0169effd-fdb7-40b0-9134-5dc6ce52732a" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_7b90986a-6fa8-4cd8-b7b2-5f4907c846ea" xlink:to="loc_us-gaap_ClassOfStockDomain_0169effd-fdb7-40b0-9134-5dc6ce52732a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_125cfe00-865f-461a-a71e-99de16d59359" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_0169effd-fdb7-40b0-9134-5dc6ce52732a" xlink:to="loc_us-gaap_CommonClassAMember_125cfe00-865f-461a-a71e-99de16d59359" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassBMember_649718a1-24fb-47b3-9925-44d8fcc7aeb7" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_CommonClassBMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_0169effd-fdb7-40b0-9134-5dc6ce52732a" xlink:to="loc_us-gaap_CommonClassBMember_649718a1-24fb-47b3-9925-44d8fcc7aeb7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_67041e8c-a376-4bd6-90b5-4f6de6a8e654" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEarningsPerShareBasicByCommonClassTable_ef8ca422-27d7-4149-a410-0a71d2eb775c" xlink:to="loc_us-gaap_AwardTypeAxis_67041e8c-a376-4bd6-90b5-4f6de6a8e654" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_67041e8c-a376-4bd6-90b5-4f6de6a8e654_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_67041e8c-a376-4bd6-90b5-4f6de6a8e654" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_67041e8c-a376-4bd6-90b5-4f6de6a8e654_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_df17d2de-5c43-4a38-9011-ec6eb8170fd9" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_67041e8c-a376-4bd6-90b5-4f6de6a8e654" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_df17d2de-5c43-4a38-9011-ec6eb8170fd9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_7c2f9d59-eb8b-4d14-bfbb-6696279d4764" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_df17d2de-5c43-4a38-9011-ec6eb8170fd9" xlink:to="loc_us-gaap_EmployeeStockOptionMember_7c2f9d59-eb8b-4d14-bfbb-6696279d4764" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ddog_SharesSubjectToEmployeeStockPurchasePlanMember_cc7983f4-deb8-49ec-add0-84d29ef5f22d" xlink:href="ddog-20210630.xsd#ddog_SharesSubjectToEmployeeStockPurchasePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_df17d2de-5c43-4a38-9011-ec6eb8170fd9" xlink:to="loc_ddog_SharesSubjectToEmployeeStockPurchasePlanMember_cc7983f4-deb8-49ec-add0-84d29ef5f22d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ddog_UnvestedEarlyExercisesAwardsMember_55fd9ebd-4f8d-48fe-b118-f56f69ce7408" xlink:href="ddog-20210630.xsd#ddog_UnvestedEarlyExercisesAwardsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_df17d2de-5c43-4a38-9011-ec6eb8170fd9" xlink:to="loc_ddog_UnvestedEarlyExercisesAwardsMember_55fd9ebd-4f8d-48fe-b118-f56f69ce7408" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_d37268f9-fdea-40a7-a96c-87202189df82" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_df17d2de-5c43-4a38-9011-ec6eb8170fd9" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_d37268f9-fdea-40a7-a96c-87202189df82" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockMember_4ada505d-eb88-4b4e-9f46-1146793b79c0" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_RestrictedStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_df17d2de-5c43-4a38-9011-ec6eb8170fd9" xlink:to="loc_us-gaap_RestrictedStockMember_4ada505d-eb88-4b4e-9f46-1146793b79c0" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.datadoghq.com/role/NetLossIncomePerShareScheduleofPotentiallyDilutiveSecuritiesnotIncludedinDilutedPerShareCalculationsDetails" xlink:type="simple" xlink:href="ddog-20210630.xsd#NetLossIncomePerShareScheduleofPotentiallyDilutiveSecuritiesnotIncludedinDilutedPerShareCalculationsDetails"/>
  <link:definitionLink xlink:role="http://www.datadoghq.com/role/NetLossIncomePerShareScheduleofPotentiallyDilutiveSecuritiesnotIncludedinDilutedPerShareCalculationsDetails" xlink:type="extended" id="i3f20723e7b1e4cd1a2be3f7decc92c85_NetLossIncomePerShareScheduleofPotentiallyDilutiveSecuritiesnotIncludedinDilutedPerShareCalculationsDetails">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_27ad9a52-7e9a-408f-a45c-8ef33228fa0e" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_04f4fbd1-cb9e-4bea-a869-f75b43d07f57" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_27ad9a52-7e9a-408f-a45c-8ef33228fa0e" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_04f4fbd1-cb9e-4bea-a869-f75b43d07f57" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_c73a1d1c-a4b6-4dc2-b19e-87a165b3fa80" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_27ad9a52-7e9a-408f-a45c-8ef33228fa0e" xlink:to="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_c73a1d1c-a4b6-4dc2-b19e-87a165b3fa80" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_267733b7-e614-4083-8174-70e7377a41b2" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_c73a1d1c-a4b6-4dc2-b19e-87a165b3fa80" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_267733b7-e614-4083-8174-70e7377a41b2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_267733b7-e614-4083-8174-70e7377a41b2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_267733b7-e614-4083-8174-70e7377a41b2" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_267733b7-e614-4083-8174-70e7377a41b2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_f05bffe1-65b5-4937-b512-501bfc6e61fc" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_267733b7-e614-4083-8174-70e7377a41b2" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_f05bffe1-65b5-4937-b512-501bfc6e61fc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ddog_EmployeeStockOptionAndRestrictedStockUnitMember_8b3d5317-46a9-427a-a9f1-2b39f45bf825" xlink:href="ddog-20210630.xsd#ddog_EmployeeStockOptionAndRestrictedStockUnitMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_f05bffe1-65b5-4937-b512-501bfc6e61fc" xlink:to="loc_ddog_EmployeeStockOptionAndRestrictedStockUnitMember_8b3d5317-46a9-427a-a9f1-2b39f45bf825" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ddog_UnvestedEarlyExercisedStockOptionsAndRestrictedStockMember_161dba1f-f68f-4be2-9339-12ead896b3a6" xlink:href="ddog-20210630.xsd#ddog_UnvestedEarlyExercisedStockOptionsAndRestrictedStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_f05bffe1-65b5-4937-b512-501bfc6e61fc" xlink:to="loc_ddog_UnvestedEarlyExercisedStockOptionsAndRestrictedStockMember_161dba1f-f68f-4be2-9339-12ead896b3a6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ddog_SharesSubjectToEmployeeStockPurchasePlanMember_2b63e03b-c56e-42ee-aa7b-3245f0116e9d" xlink:href="ddog-20210630.xsd#ddog_SharesSubjectToEmployeeStockPurchasePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_f05bffe1-65b5-4937-b512-501bfc6e61fc" xlink:to="loc_ddog_SharesSubjectToEmployeeStockPurchasePlanMember_2b63e03b-c56e-42ee-aa7b-3245f0116e9d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ddog_SharesIssuableUponConversionOfTheConvertibleSeniorNotesMember_3d49baaa-f8f2-4e5e-980c-02b21a41f883" xlink:href="ddog-20210630.xsd#ddog_SharesIssuableUponConversionOfTheConvertibleSeniorNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_f05bffe1-65b5-4937-b512-501bfc6e61fc" xlink:to="loc_ddog_SharesIssuableUponConversionOfTheConvertibleSeniorNotesMember_3d49baaa-f8f2-4e5e-980c-02b21a41f883" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fasb.org/us-gaap/role/eedm/ExtensibleEnumerationLists" xlink:type="simple" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-roles-2021-01-31.xsd#eedm"/>
  <link:definitionLink xlink:role="http://fasb.org/us-gaap/role/eedm/ExtensibleEnumerationLists" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfAdoptionMember" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_TypeOfAdoptionMember"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountingStandardsUpdate202006Member" xlink:href="https://xbrl.fasb.org/us-gaap/2021/elts/us-gaap-2021-01-31.xsd#us-gaap_AccountingStandardsUpdate202006Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfAdoptionMember" xlink:to="loc_us-gaap_AccountingStandardsUpdate202006Member" xlink:type="arc" order="0"/>
  </link:definitionLink>
</link:linkbase>
