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

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2025 Workiva-->
<!--r:447c73de-d963-41ce-921f-8895802caa14,g:0b96abf8-1d6c-4b23-9e48-f581cd9711d9-->
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:nmih="http://www.nationalmi.com/20250327" xmlns:xbrli="http://www.xbrl.org/2003/instance" xmlns:dtr-types1="http://www.xbrl.org/dtr/type/2020-01-21" attributeFormDefault="unqualified" elementFormDefault="qualified" targetNamespace="http://www.nationalmi.com/20250327">
  <xs:import namespace="http://www.xbrl.org/2003/instance" schemaLocation="http://www.xbrl.org/2003/xbrl-instance-2003-12-31.xsd"/>
  <xs:import namespace="http://www.xbrl.org/2003/linkbase" schemaLocation="http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd"/>
  <xs:import namespace="http://www.xbrl.org/dtr/type/2020-01-21" schemaLocation="https://www.xbrl.org/dtr/type/2020-01-21/types.xsd"/>
  <xs:import namespace="http://xbrl.sec.gov/dei-sub/2023" schemaLocation="https://xbrl.sec.gov/dei/2023/dei-sub-2023.xsd"/>
  <xs:import namespace="http://xbrl.sec.gov/ecd-sub/2023" schemaLocation="https://xbrl.sec.gov/ecd/2023/ecd-sub-2023.xsd"/>
  <xs:annotation>
    <xs:appinfo>
      <link:linkbaseRef xmlns:xlink="http://www.w3.org/1999/xlink" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:href="nmih-20250327_pre.xml" xlink:role="http://www.xbrl.org/2003/role/presentationLinkbaseRef" xlink:type="simple"/>
      <link:linkbaseRef xmlns:xlink="http://www.w3.org/1999/xlink" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:href="nmih-20250327_def.xml" xlink:role="http://www.xbrl.org/2003/role/definitionLinkbaseRef" xlink:type="simple"/>
      <link:linkbaseRef xmlns:xlink="http://www.w3.org/1999/xlink" xlink:arcrole="http://www.w3.org/1999/xlink/properties/linkbase" xlink:href="nmih-20250327_lab.xml" xlink:role="http://www.xbrl.org/2003/role/labelLinkbaseRef" xlink:type="simple"/>
    </xs:appinfo>
  </xs:annotation>
  <xs:element id="nmih_AdjustmentEquityAwardsReportedMember" abstract="true" name="AdjustmentEquityAwardsReportedMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="nmih_AdjustmentYearEndFairValueOfOutstandingAndUnvestedEquityAwardsGrantedInTheApplicableYearMember" abstract="true" name="AdjustmentYearEndFairValueOfOutstandingAndUnvestedEquityAwardsGrantedInTheApplicableYearMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="nmih_AdjustmentYearOverYearChangeInFairValueOfOutstandingAndUnvestedEquityAwardsGrantedInPriorYearsMember" abstract="true" name="AdjustmentYearOverYearChangeInFairValueOfOutstandingAndUnvestedEquityAwardsGrantedInPriorYearsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="nmih_AdjustmentYearOverYearChangeInFairValueOfEquityAwardsGrantedInPriorYearsThatVestedInTheYearMember" abstract="true" name="AdjustmentYearOverYearChangeInFairValueOfEquityAwardsGrantedInPriorYearsThatVestedInTheYearMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
</xs:schema>
