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

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:019ca138-51f1-727b-9cff-9b9fc7676120,g:f8622457-3818-4cde-b0f4-b67367a082c3-->
<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://opendoor.com/role/Cover" xlink:type="simple" xlink:href="open-20260507.xsd#Cover"/>
  <link:definitionLink xlink:role="http://opendoor.com/role/Cover" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationLineItems_019ca138-51f1-72b0-be5d-f9907475f383" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_DocumentInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationTable_019ca138-51f1-7225-8b0d-20b4b30e2e58" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_DocumentInformationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dei_DocumentInformationLineItems_019ca138-51f1-72b0-be5d-f9907475f383" xlink:to="loc_dei_DocumentInformationTable_019ca138-51f1-7225-8b0d-20b4b30e2e58" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019ca138-51f1-749b-9320-bc63e9b9fea1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_DocumentInformationTable_019ca138-51f1-7225-8b0d-20b4b30e2e58" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019ca138-51f1-749b-9320-bc63e9b9fea1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019ca138-51f1-749b-9320-bc63e9b9fea1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019ca138-51f1-749b-9320-bc63e9b9fea1" xlink:to="loc_us-gaap_ClassOfStockDomain_019ca138-51f1-749b-9320-bc63e9b9fea1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019ca138-51f1-769c-a79a-332c7913aa77" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019ca138-51f1-749b-9320-bc63e9b9fea1" xlink:to="loc_us-gaap_ClassOfStockDomain_019ca138-51f1-769c-a79a-332c7913aa77" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019ca138-51f1-720f-8418-a6e5a951b617" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019ca138-51f1-769c-a79a-332c7913aa77" xlink:to="loc_us-gaap_CommonStockMember_019ca138-51f1-720f-8418-a6e5a951b617" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_open_SeriesAWarrantsMember_019ca138-51f1-7003-a09e-79b909cf94aa" xlink:href="open-20260507.xsd#open_SeriesAWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019ca138-51f1-769c-a79a-332c7913aa77" xlink:to="loc_open_SeriesAWarrantsMember_019ca138-51f1-7003-a09e-79b909cf94aa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_open_SeriesKWarrantsMember_019ca138-51f1-7185-8c9b-84395fd92848" xlink:href="open-20260507.xsd#open_SeriesKWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019ca138-51f1-769c-a79a-332c7913aa77" xlink:to="loc_open_SeriesKWarrantsMember_019ca138-51f1-7185-8c9b-84395fd92848" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_open_SeriesZWarrantsMember_019ca138-51f1-7da0-85c3-fe7418fdf9ca" xlink:href="open-20260507.xsd#open_SeriesZWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019ca138-51f1-769c-a79a-332c7913aa77" xlink:to="loc_open_SeriesZWarrantsMember_019ca138-51f1-7da0-85c3-fe7418fdf9ca" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_Security12bTitle_019ca138-51f1-74e5-861c-de819f36d4cf" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_Security12bTitle"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ca138-51f1-72b0-be5d-f9907475f383" xlink:to="loc_dei_Security12bTitle_019ca138-51f1-74e5-861c-de819f36d4cf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentType_019ca138-51f1-7f72-9168-640ca3110ae7" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_DocumentType"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ca138-51f1-72b0-be5d-f9907475f383" xlink:to="loc_dei_DocumentType_019ca138-51f1-7f72-9168-640ca3110ae7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentPeriodEndDate_019ca138-51f1-7633-ab3d-6ea397793008" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_DocumentPeriodEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ca138-51f1-72b0-be5d-f9907475f383" xlink:to="loc_dei_DocumentPeriodEndDate_019ca138-51f1-7633-ab3d-6ea397793008" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityRegistrantName_019ca138-51f1-7468-9dcf-f2b8ffd4e3bb" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityRegistrantName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ca138-51f1-72b0-be5d-f9907475f383" xlink:to="loc_dei_EntityRegistrantName_019ca138-51f1-7468-9dcf-f2b8ffd4e3bb" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityIncorporationStateCountryCode_019ca138-51f1-795c-9e34-12686a6cb90e" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityIncorporationStateCountryCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ca138-51f1-72b0-be5d-f9907475f383" xlink:to="loc_dei_EntityIncorporationStateCountryCode_019ca138-51f1-795c-9e34-12686a6cb90e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFileNumber_019ca138-51f1-73c9-b837-0fff539f8a10" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityFileNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ca138-51f1-72b0-be5d-f9907475f383" xlink:to="loc_dei_EntityFileNumber_019ca138-51f1-73c9-b837-0fff539f8a10" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityTaxIdentificationNumber_019ca138-51f1-7ddc-82e4-99f447ecb97b" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityTaxIdentificationNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ca138-51f1-72b0-be5d-f9907475f383" xlink:to="loc_dei_EntityTaxIdentificationNumber_019ca138-51f1-7ddc-82e4-99f447ecb97b" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine1_019ca138-51f1-7028-a47e-5a6e8b801124" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityAddressAddressLine1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ca138-51f1-72b0-be5d-f9907475f383" xlink:to="loc_dei_EntityAddressAddressLine1_019ca138-51f1-7028-a47e-5a6e8b801124" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine2_019ca138-51f1-7b35-8986-839cce8e3e90" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityAddressAddressLine2"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ca138-51f1-72b0-be5d-f9907475f383" xlink:to="loc_dei_EntityAddressAddressLine2_019ca138-51f1-7b35-8986-839cce8e3e90" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressCityOrTown_019ca138-51f1-75ef-bae9-1862c390708b" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityAddressCityOrTown"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ca138-51f1-72b0-be5d-f9907475f383" xlink:to="loc_dei_EntityAddressCityOrTown_019ca138-51f1-75ef-bae9-1862c390708b" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressStateOrProvince_019ca138-51f1-7878-a5ce-f3902b008600" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityAddressStateOrProvince"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ca138-51f1-72b0-be5d-f9907475f383" xlink:to="loc_dei_EntityAddressStateOrProvince_019ca138-51f1-7878-a5ce-f3902b008600" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressPostalZipCode_019ca138-51f1-7c02-968f-62824b9c704e" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityAddressPostalZipCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ca138-51f1-72b0-be5d-f9907475f383" xlink:to="loc_dei_EntityAddressPostalZipCode_019ca138-51f1-7c02-968f-62824b9c704e" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CityAreaCode_019ca138-51f1-7a7c-8f05-a8b11aa70938" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_CityAreaCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ca138-51f1-72b0-be5d-f9907475f383" xlink:to="loc_dei_CityAreaCode_019ca138-51f1-7a7c-8f05-a8b11aa70938" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LocalPhoneNumber_019ca138-51f1-7749-b216-3df599e24593" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_LocalPhoneNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ca138-51f1-72b0-be5d-f9907475f383" xlink:to="loc_dei_LocalPhoneNumber_019ca138-51f1-7749-b216-3df599e24593" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_WrittenCommunications_019ca138-51f1-7f66-88c6-2ffc4bed50f2" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_WrittenCommunications"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ca138-51f1-72b0-be5d-f9907475f383" xlink:to="loc_dei_WrittenCommunications_019ca138-51f1-7f66-88c6-2ffc4bed50f2" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SolicitingMaterial_019ca138-51f1-795c-84e1-31aa4be859be" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_SolicitingMaterial"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ca138-51f1-72b0-be5d-f9907475f383" xlink:to="loc_dei_SolicitingMaterial_019ca138-51f1-795c-84e1-31aa4be859be" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_PreCommencementTenderOffer_019ca138-51f1-7b9e-b189-5058695717e2" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_PreCommencementTenderOffer"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ca138-51f1-72b0-be5d-f9907475f383" xlink:to="loc_dei_PreCommencementTenderOffer_019ca138-51f1-7b9e-b189-5058695717e2" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_PreCommencementIssuerTenderOffer_019ca138-51f1-7f86-96eb-f2853d4fcb89" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_PreCommencementIssuerTenderOffer"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ca138-51f1-72b0-be5d-f9907475f383" xlink:to="loc_dei_PreCommencementIssuerTenderOffer_019ca138-51f1-7f86-96eb-f2853d4fcb89" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_Security12bTitle_019ca138-51f1-7a78-a08c-5f3179863569" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_Security12bTitle"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_TradingSymbol_019ca138-51f1-74d0-900a-0851279b51d4" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_TradingSymbol"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ca138-51f1-72b0-be5d-f9907475f383" xlink:to="loc_dei_TradingSymbol_019ca138-51f1-74d0-900a-0851279b51d4" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SecurityExchangeName_019ca138-51f1-776e-a3ab-381887495294" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_SecurityExchangeName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ca138-51f1-72b0-be5d-f9907475f383" xlink:to="loc_dei_SecurityExchangeName_019ca138-51f1-776e-a3ab-381887495294" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityEmergingGrowthCompany_019ca138-51f1-75a2-819c-be28a67975e8" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityEmergingGrowthCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ca138-51f1-72b0-be5d-f9907475f383" xlink:to="loc_dei_EntityEmergingGrowthCompany_019ca138-51f1-75a2-819c-be28a67975e8" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCentralIndexKey_019ca138-51f1-7044-a733-5a8292845f9c" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityCentralIndexKey"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ca138-51f1-72b0-be5d-f9907475f383" xlink:to="loc_dei_EntityCentralIndexKey_019ca138-51f1-7044-a733-5a8292845f9c" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AmendmentFlag_019ca138-51f1-735b-a6a5-df01d22585f9" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_AmendmentFlag"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ca138-51f1-72b0-be5d-f9907475f383" xlink:to="loc_dei_AmendmentFlag_019ca138-51f1-735b-a6a5-df01d22585f9" xlink:type="arc" order="23"/>
  </link:definitionLink>
</link:linkbase>
