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

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:019f1f97-283d-792d-aca8-123c2e4a7206,g:ee8fa8ce-88ac-4688-8223-c3b942efb666-->
<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.armourreit.com/role/CoverDocument" xlink:type="simple" xlink:href="arr-20260721.xsd#CoverDocument"/>
  <link:definitionLink xlink:role="http://www.armourreit.com/role/CoverDocument" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationLineItems_019f1f97-283d-757c-8e00-88180e920ea5" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationTable_019f1f97-283d-7695-b253-f6966e648b5a" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentInformationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dei_DocumentInformationLineItems_019f1f97-283d-757c-8e00-88180e920ea5" xlink:to="loc_dei_DocumentInformationTable_019f1f97-283d-7695-b253-f6966e648b5a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019f1f97-283d-747e-9456-880e4a5e5a95" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_DocumentInformationTable_019f1f97-283d-7695-b253-f6966e648b5a" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019f1f97-283d-747e-9456-880e4a5e5a95" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019f1f97-283d-747e-9456-880e4a5e5a95_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019f1f97-283d-747e-9456-880e4a5e5a95" xlink:to="loc_us-gaap_ClassOfStockDomain_019f1f97-283d-747e-9456-880e4a5e5a95_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019f1f97-283d-74de-b7cd-abeb39ba68b3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019f1f97-283d-747e-9456-880e4a5e5a95" xlink:to="loc_us-gaap_ClassOfStockDomain_019f1f97-283d-74de-b7cd-abeb39ba68b3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_arr_PreferredClassCMember_019f1f97-283d-78e3-a79a-e6aaba7642eb" xlink:href="arr-20260721.xsd#arr_PreferredClassCMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019f1f97-283d-74de-b7cd-abeb39ba68b3" xlink:to="loc_arr_PreferredClassCMember_019f1f97-283d-78e3-a79a-e6aaba7642eb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019f1f97-283d-70a2-b38b-1afe8ff3143f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019f1f97-283d-74de-b7cd-abeb39ba68b3" xlink:to="loc_us-gaap_CommonStockMember_019f1f97-283d-70a2-b38b-1afe8ff3143f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentType_019f1f97-283d-7b1b-b96b-283591f8763e" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentType"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019f1f97-283d-757c-8e00-88180e920ea5" xlink:to="loc_dei_DocumentType_019f1f97-283d-7b1b-b96b-283591f8763e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentPeriodEndDate_019f1f97-283d-7197-ac4b-8a7ff17c6ff7" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentPeriodEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019f1f97-283d-757c-8e00-88180e920ea5" xlink:to="loc_dei_DocumentPeriodEndDate_019f1f97-283d-7197-ac4b-8a7ff17c6ff7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityRegistrantName_019f1f97-283d-7652-aae2-33256d094000" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityRegistrantName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019f1f97-283d-757c-8e00-88180e920ea5" xlink:to="loc_dei_EntityRegistrantName_019f1f97-283d-7652-aae2-33256d094000" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityIncorporationStateCountryCode_019f1f97-283d-76de-8be4-a04a43d0f697" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityIncorporationStateCountryCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019f1f97-283d-757c-8e00-88180e920ea5" xlink:to="loc_dei_EntityIncorporationStateCountryCode_019f1f97-283d-76de-8be4-a04a43d0f697" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFileNumber_019f1f97-283d-7dae-8e9a-03e92cdeb398" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityFileNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019f1f97-283d-757c-8e00-88180e920ea5" xlink:to="loc_dei_EntityFileNumber_019f1f97-283d-7dae-8e9a-03e92cdeb398" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityTaxIdentificationNumber_019f1f97-283d-73bc-8d1e-deeafb7b4462" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityTaxIdentificationNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019f1f97-283d-757c-8e00-88180e920ea5" xlink:to="loc_dei_EntityTaxIdentificationNumber_019f1f97-283d-73bc-8d1e-deeafb7b4462" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine1_019f1f97-283d-757b-9e10-cf34027e52dc" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressAddressLine1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019f1f97-283d-757c-8e00-88180e920ea5" xlink:to="loc_dei_EntityAddressAddressLine1_019f1f97-283d-757b-9e10-cf34027e52dc" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressCityOrTown_019f1f97-283d-7a48-9f92-44f2d2de463f" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressCityOrTown"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019f1f97-283d-757c-8e00-88180e920ea5" xlink:to="loc_dei_EntityAddressCityOrTown_019f1f97-283d-7a48-9f92-44f2d2de463f" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressStateOrProvince_019f1f97-283d-72c0-bd6d-2ef9fab02ffc" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressStateOrProvince"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019f1f97-283d-757c-8e00-88180e920ea5" xlink:to="loc_dei_EntityAddressStateOrProvince_019f1f97-283d-72c0-bd6d-2ef9fab02ffc" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressPostalZipCode_019f1f97-283d-731e-b788-7c4a12ccb7be" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressPostalZipCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019f1f97-283d-757c-8e00-88180e920ea5" xlink:to="loc_dei_EntityAddressPostalZipCode_019f1f97-283d-731e-b788-7c4a12ccb7be" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CityAreaCode_019f1f97-283d-70a9-8f3e-4ab83b8336e8" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_CityAreaCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019f1f97-283d-757c-8e00-88180e920ea5" xlink:to="loc_dei_CityAreaCode_019f1f97-283d-70a9-8f3e-4ab83b8336e8" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LocalPhoneNumber_019f1f97-283d-70e2-b4e4-553bfd2ed284" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LocalPhoneNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019f1f97-283d-757c-8e00-88180e920ea5" xlink:to="loc_dei_LocalPhoneNumber_019f1f97-283d-70e2-b4e4-553bfd2ed284" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_WrittenCommunications_019f1f97-283d-799b-8225-55457ab990ab" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_WrittenCommunications"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019f1f97-283d-757c-8e00-88180e920ea5" xlink:to="loc_dei_WrittenCommunications_019f1f97-283d-799b-8225-55457ab990ab" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SolicitingMaterial_019f1f97-283d-7738-aa23-1a28dc68a89e" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_SolicitingMaterial"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019f1f97-283d-757c-8e00-88180e920ea5" xlink:to="loc_dei_SolicitingMaterial_019f1f97-283d-7738-aa23-1a28dc68a89e" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_PreCommencementTenderOffer_019f1f97-283d-74d0-8c9a-bb9d09755d6d" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_PreCommencementTenderOffer"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019f1f97-283d-757c-8e00-88180e920ea5" xlink:to="loc_dei_PreCommencementTenderOffer_019f1f97-283d-74d0-8c9a-bb9d09755d6d" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_PreCommencementIssuerTenderOffer_019f1f97-283d-7990-b422-148adb0b1725" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_PreCommencementIssuerTenderOffer"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019f1f97-283d-757c-8e00-88180e920ea5" xlink:to="loc_dei_PreCommencementIssuerTenderOffer_019f1f97-283d-7990-b422-148adb0b1725" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_Security12bTitle_019f1f97-283d-7f4e-9498-e9b1b11f6fc9" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_Security12bTitle"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019f1f97-283d-757c-8e00-88180e920ea5" xlink:to="loc_dei_Security12bTitle_019f1f97-283d-7f4e-9498-e9b1b11f6fc9" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_TradingSymbol_019f1f97-283d-7d58-9b78-47090ec2cf11" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_TradingSymbol"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019f1f97-283d-757c-8e00-88180e920ea5" xlink:to="loc_dei_TradingSymbol_019f1f97-283d-7d58-9b78-47090ec2cf11" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SecurityExchangeName_019f1f97-283d-7541-a142-64fd7249c152" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_SecurityExchangeName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019f1f97-283d-757c-8e00-88180e920ea5" xlink:to="loc_dei_SecurityExchangeName_019f1f97-283d-7541-a142-64fd7249c152" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityEmergingGrowthCompany_019f1f97-283d-7a06-bc4c-238fa4243098" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityEmergingGrowthCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019f1f97-283d-757c-8e00-88180e920ea5" xlink:to="loc_dei_EntityEmergingGrowthCompany_019f1f97-283d-7a06-bc4c-238fa4243098" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCentralIndexKey_019f1f97-283d-783b-b22c-e38f0bfbc75c" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityCentralIndexKey"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019f1f97-283d-757c-8e00-88180e920ea5" xlink:to="loc_dei_EntityCentralIndexKey_019f1f97-283d-783b-b22c-e38f0bfbc75c" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AmendmentFlag_019f1f97-283d-7add-b353-dd8b76f08a05" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_AmendmentFlag"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019f1f97-283d-757c-8e00-88180e920ea5" xlink:to="loc_dei_AmendmentFlag_019f1f97-283d-7add-b353-dd8b76f08a05" xlink:type="arc" order="21"/>
  </link:definitionLink>
</link:linkbase>
