diff --git a/client/app/bundles/course/statistics/pages/StatisticsIndex/students/StudentStatisticsTable.tsx b/client/app/bundles/course/statistics/pages/StatisticsIndex/students/StudentStatisticsTable.tsx
index 5f22c48ce17..038540e0c4b 100644
--- a/client/app/bundles/course/statistics/pages/StatisticsIndex/students/StudentStatisticsTable.tsx
+++ b/client/app/bundles/course/statistics/pages/StatisticsIndex/students/StudentStatisticsTable.tsx
@@ -61,7 +61,7 @@ const translations = defineMessages({
   },
   searchBar: {
     id: 'course.statistics.StatisticsIndex.students.searchBar',
-    defaultMessage: 'Search by Student Name or Student Type',
+    defaultMessage: 'Search by Student Name, Student Type or External ID',
   },
 });
 
diff --git a/client/app/bundles/course/user-invitations/components/tables/UserInvitationsTable.tsx b/client/app/bundles/course/user-invitations/components/tables/UserInvitationsTable.tsx
index c24b976f1f8..89c4c7694a0 100644
--- a/client/app/bundles/course/user-invitations/components/tables/UserInvitationsTable.tsx
+++ b/client/app/bundles/course/user-invitations/components/tables/UserInvitationsTable.tsx
@@ -170,8 +170,8 @@ const UserInvitationsTable: FC<Props> = (props) => {
             of: 'externalId',
             title: t(tableTranslations.externalId),
             sortable: false,
-            searchable: false,
-            cell: (datum) => datum.externalId ?? '',
+            searchable: true,
+            cell: (datum) => datum.externalId ?? null,
           } satisfies ColumnTemplate<InvitationRowData>,
         ]
       : []),
@@ -280,6 +280,9 @@ const UserInvitationsTable: FC<Props> = (props) => {
       data={processedInvitations}
       getRowId={(datum) => datum.id.toString()}
       indexing={{ indices: true }}
+      search={{
+        searchPlaceholder: t(translations.searchText),
+      }}
       sort={{
         initially: { by: 'status', order: 'asc' },
       }}
diff --git a/client/app/bundles/course/user-invitations/components/tables/__test__/UserInvitationsTable.test.tsx b/client/app/bundles/course/user-invitations/components/tables/__test__/UserInvitationsTable.test.tsx
new file mode 100644
index 00000000000..62bde5be532
--- /dev/null
+++ b/client/app/bundles/course/user-invitations/components/tables/__test__/UserInvitationsTable.test.tsx
@@ -0,0 +1,115 @@
+import userEvent from '@testing-library/user-event';
+import { render, screen, waitForElementToBeRemoved } from 'test-utils';
+import { InvitationMiniEntity } from 'types/course/userInvitations';
+
+import UserInvitationsTable from '../UserInvitationsTable';
+
+const baseInvitation: InvitationMiniEntity = {
+  id: 1,
+  name: 'Alice Lim',
+  email: 'alice@example.com',
+  externalId: null,
+  role: 'student',
+  phantom: false,
+  confirmed: false,
+  isRetryable: true,
+  invitationKey: 'KEY001',
+  sentAt: '2024-01-01T00:00:00Z',
+  confirmedAt: null,
+};
+
+const SEARCH_PLACEHOLDER = 'Search by name, email or external ID';
+
+describe('<UserInvitationsTable />', () => {
+  describe('search', () => {
+    it('filters invitations by external ID', async () => {
+      const user = userEvent.setup();
+      const invitations: InvitationMiniEntity[] = [
+        {
+          ...baseInvitation,
+          id: 1,
+          name: 'Alice Lim',
+          externalId: 'EXT-ALICE',
+        },
+        {
+          ...baseInvitation,
+          id: 2,
+          name: 'Bob Tan',
+          email: 'bob@example.com',
+          externalId: 'EXT-BOB',
+        },
+      ];
+
+      render(<UserInvitationsTable invitations={invitations} />);
+      await waitForElementToBeRemoved(() => screen.queryByRole('progressbar'));
+
+      await user.type(
+        screen.getByPlaceholderText(SEARCH_PLACEHOLDER),
+        'EXT-ALICE',
+      );
+
+      expect(screen.getByText('Alice Lim')).toBeInTheDocument();
+      expect(screen.queryByText('Bob Tan')).not.toBeInTheDocument();
+    });
+
+    it('searches external ID case-insensitively', async () => {
+      const user = userEvent.setup();
+      const invitations: InvitationMiniEntity[] = [
+        {
+          ...baseInvitation,
+          id: 1,
+          name: 'Alice Lim',
+          externalId: 'ext-alice',
+        },
+        {
+          ...baseInvitation,
+          id: 2,
+          name: 'Bob Tan',
+          email: 'bob@example.com',
+          externalId: 'EXT-BOB',
+        },
+      ];
+
+      render(<UserInvitationsTable invitations={invitations} />);
+      await waitForElementToBeRemoved(() => screen.queryByRole('progressbar'));
+
+      await user.type(
+        screen.getByPlaceholderText(SEARCH_PLACEHOLDER),
+        'EXT-ALICE',
+      );
+
+      expect(screen.getByText('Alice Lim')).toBeInTheDocument();
+      expect(screen.queryByText('Bob Tan')).not.toBeInTheDocument();
+    });
+
+    it('shows all invitations when search is cleared', async () => {
+      const user = userEvent.setup();
+      const invitations: InvitationMiniEntity[] = [
+        {
+          ...baseInvitation,
+          id: 1,
+          name: 'Alice Lim',
+          externalId: 'EXT-ALICE',
+        },
+        {
+          ...baseInvitation,
+          id: 2,
+          name: 'Bob Tan',
+          email: 'bob@example.com',
+          externalId: 'EXT-BOB',
+        },
+      ];
+
+      render(<UserInvitationsTable invitations={invitations} />);
+      await waitForElementToBeRemoved(() => screen.queryByRole('progressbar'));
+
+      const searchInput = screen.getByPlaceholderText(SEARCH_PLACEHOLDER);
+      await user.type(searchInput, 'EXT-ALICE');
+      expect(screen.queryByText('Bob Tan')).not.toBeInTheDocument();
+
+      await user.clear(searchInput);
+      expect(screen.getByText('Alice Lim')).toBeInTheDocument();
+      expect(screen.getByText('Bob Tan')).toBeInTheDocument();
+    });
+  });
+});
diff --git a/client/app/bundles/course/user-invitations/translations.ts b/client/app/bundles/course/user-invitations/translations.ts
index c3c249f6b4c..0569076b635 100644
--- a/client/app/bundles/course/user-invitations/translations.ts
+++ b/client/app/bundles/course/user-invitations/translations.ts
@@ -22,6 +22,10 @@ const translations = defineMessages({
     id: 'course.userInvitations.UserInvitationsTable.noInvitations',
     defaultMessage: 'There are no invitations.',
   },
+  searchText: {
+    id: 'course.userInvitations.UserInvitationsTable.searchText',
+    defaultMessage: 'Search by name, email or external ID',
+  },
   pending: {
     id: 'course.userInvitations.UserInvitationsTable.pending',
     defaultMessage: 'Pending',
diff --git a/client/app/bundles/course/users/components/tables/ManageUsersTable/__test__/index.test.tsx b/client/app/bundles/course/users/components/tables/ManageUsersTable/__test__/index.test.tsx
new file mode 100644
index 00000000000..fdbaedfc26c
--- /dev/null
+++ b/client/app/bundles/course/users/components/tables/ManageUsersTable/__test__/index.test.tsx
@@ -0,0 +1,99 @@
+import userEvent from '@testing-library/user-event';
+import { render, screen, waitForElementToBeRemoved } from 'test-utils';
+import { CourseUserMiniEntity } from 'types/course/courseUsers';
+
+import ManageUsersTable from '../index';
+
+const baseUser: CourseUserMiniEntity = {
+  id: 1,
+  name: 'Alice Lim',
+  email: 'alice@example.com',
+  role: 'student',
+};
+
+const SEARCH_PLACEHOLDER = 'Search by name, email or external ID';
+
+describe('<ManageUsersTable />', () => {
+  describe('search', () => {
+    it('filters users by external ID', async () => {
+      const user = userEvent.setup();
+      const users: CourseUserMiniEntity[] = [
+        { ...baseUser, id: 1, name: 'Alice Lim', externalId: 'EXT-ALICE' },
+        {
+          ...baseUser,
+          id: 2,
+          name: 'Bob Tan',
+          email: 'bob@example.com',
+          externalId: 'EXT-BOB',
+        },
+      ];
+
+      render(
+        <ManageUsersTable csvDownloadFilename="users.csv" users={users} />,
+      );
+      await waitForElementToBeRemoved(() => screen.queryByRole('progressbar'));
+
+      await user.type(
+        screen.getByPlaceholderText(SEARCH_PLACEHOLDER),
+        'EXT-ALICE',
+      );
+
+      expect(screen.getByText('Alice Lim')).toBeInTheDocument();
+      expect(screen.queryByText('Bob Tan')).not.toBeInTheDocument();
+    });
+
+    it('searches external ID case-insensitively', async () => {
+      const user = userEvent.setup();
+      const users: CourseUserMiniEntity[] = [
+        { ...baseUser, id: 1, name: 'Alice Lim', externalId: 'ext-alice' },
+        {
+          ...baseUser,
+          id: 2,
+          name: 'Bob Tan',
+          email: 'bob@example.com',
+          externalId: 'EXT-BOB',
+        },
+      ];
+
+      render(
+        <ManageUsersTable csvDownloadFilename="users.csv" users={users} />,
+      );
+      await waitForElementToBeRemoved(() => screen.queryByRole('progressbar'));
+
+      await user.type(
+        screen.getByPlaceholderText(SEARCH_PLACEHOLDER),
+        'EXT-ALICE',
+      );
+
+      expect(screen.getByText('Alice Lim')).toBeInTheDocument();
+      expect(screen.queryByText('Bob Tan')).not.toBeInTheDocument();
+    });
+
+    it('shows all users when search is cleared', async () => {
+      const user = userEvent.setup();
+      const users: CourseUserMiniEntity[] = [
+        { ...baseUser, id: 1, name: 'Alice Lim', externalId: 'EXT-ALICE' },
+        {
+          ...baseUser,
+          id: 2,
+          name: 'Bob Tan',
+          email: 'bob@example.com',
+          externalId: 'EXT-BOB',
+        },
+      ];
+
+      render(
+        <ManageUsersTable csvDownloadFilename="users.csv" users={users} />,
+      );
+      await waitForElementToBeRemoved(() => screen.queryByRole('progressbar'));
+
+      const searchInput = screen.getByPlaceholderText(SEARCH_PLACEHOLDER);
+      await user.type(searchInput, 'EXT-ALICE');
+      expect(screen.queryByText('Bob Tan')).not.toBeInTheDocument();
+
+      await user.clear(searchInput);
+      expect(screen.getByText('Alice Lim')).toBeInTheDocument();
+      expect(screen.getByText('Bob Tan')).toBeInTheDocument();
+    });
+  });
+});
diff --git a/client/app/bundles/course/users/components/tables/ManageUsersTable/index.tsx b/client/app/bundles/course/users/components/tables/ManageUsersTable/index.tsx
index 31da6ed8c16..72bf3413222 100644
--- a/client/app/bundles/course/users/components/tables/ManageUsersTable/index.tsx
+++ b/client/app/bundles/course/users/components/tables/ManageUsersTable/index.tsx
@@ -195,15 +195,11 @@ const ManageUsersTable = (props: ManageUsersTableProps): JSX.Element => {
             if (!user.name && !user.email) return false;
             if (!filterValue?.length) return true;
 
+            const query = filterValue.toLowerCase().trim();
             return (
-              user.name
-                .toLowerCase()
-                .trim()
-                .includes(filterValue.toLowerCase().trim()) ||
-              user.email
-                .toLowerCase()
-                .trim()
-                .includes(filterValue.toLowerCase().trim())
+              user.name.toLowerCase().trim().includes(query) ||
+              user.email.toLowerCase().trim().includes(query) ||
+              (user.externalId?.toLowerCase().trim().includes(query) ?? false)
             );
           },
         },
diff --git a/client/app/bundles/course/users/translations.ts b/client/app/bundles/course/users/translations.ts
index cb7aec0635d..c4e66a140b5 100644
--- a/client/app/bundles/course/users/translations.ts
+++ b/client/app/bundles/course/users/translations.ts
@@ -7,7 +7,7 @@ const translations = defineMessages({
   },
   searchText: {
     id: 'course.users.ManageUsersTable.ManageUsersTable.searchText',
-    defaultMessage: 'Search by name or email',
+    defaultMessage: 'Search by name, email or external ID',
   },
   renameSuccess: {
     id: 'course.users.ManageUsersTable.renameSuccess',
diff --git a/client/app/lib/components/table/TanStackTableBuilder/useTanStackTableBuilder.tsx b/client/app/lib/components/table/TanStackTableBuilder/useTanStackTableBuilder.tsx
index dc648e2f28e..b8544e8f937 100644
--- a/client/app/lib/components/table/TanStackTableBuilder/useTanStackTableBuilder.tsx
+++ b/client/app/lib/components/table/TanStackTableBuilder/useTanStackTableBuilder.tsx
@@ -175,6 +175,14 @@ const useTanStackTableBuilder = <D extends object>(
         props.pagination.onPaginationChange(newValue, pagination);
       }
     },
+    // TanStack's default getColumnCanGlobalFilter sniffs the first row's value
+    // type (string|number) to decide whether a column participates in global
+    // filter. When the first row has a nullable column (e.g. externalId=null),
+    // typeof null === 'object' → false, silently excluding that column from
+    // search even when the column has searchable:true / enableGlobalFilter:true.
+    // We already express intent via enableGlobalFilter, so bypass the sniff.
+    // See: https://github.com/TanStack/table/pull/6252
+    getColumnCanGlobalFilter: () => true,
     autoResetPageIndex: false,
     state: {
       rowSelection,
diff --git a/client/app/lib/components/table/__tests__/useTanStackTableBuilder.test.tsx b/client/app/lib/components/table/__tests__/useTanStackTableBuilder.test.tsx
index b8899dbf676..94f6031da08 100644
--- a/client/app/lib/components/table/__tests__/useTanStackTableBuilder.test.tsx
+++ b/client/app/lib/components/table/__tests__/useTanStackTableBuilder.test.tsx
@@ -768,6 +768,58 @@ describe('localStorage persistence', () => {
   });
 });
 
+// ---------- global search — nullable searchable column (regression) ----------
+//
+// Root cause: TanStack's default getColumnCanGlobalFilter sniffs the first row's
+// value type (string|number). When the first row has externalId=null, typeof null
+// === 'object', so TanStack silently excludes the column from global filter for
+// the entire table — even rows with a real string value are never matched.
+// Fix: override getColumnCanGlobalFilter in useReactTable to return true always,
+// relying on enableGlobalFilter (set by searchable:true/false) instead of sniffing.
+
+describe('global search — searchable column whose first row is null', () => {
+  interface StudentRow {
+    id: number;
+    name: string;
+    externalId: string | null;
+  }
+
+  const nullFirstData: StudentRow[] = [
+    { id: 1, name: 'Alice', externalId: null },
+    { id: 2, name: 'Bob', externalId: 'EXT001' },
+  ];
+
+  const searchColumns: ColumnTemplate<StudentRow>[] = [
+    { of: 'name', title: 'Name', cell: (r) => r.name, searchable: true },
+    {
+      of: 'externalId',
+      title: 'External ID',
+      cell: (r) => r.externalId ?? '',
+      searchable: true,
+    },
+  ];
+
+  it('finds rows by a searchable column value even when the first row has null for that column', () => {
+    const { result } = renderHook(
+      () =>
+        useTanStackTableBuilder<StudentRow>({
+          data: nullFirstData,
+          columns: searchColumns,
+          getRowId: (r) => r.id.toString(),
+          search: { searchPlaceholder: 'Search' },
+        }),
+      { wrapper: withStore() },
+    );
+
+    act(() => result.current.toolbar!.onSearchKeywordChange?.('EXT001'));
+
+    expect(result.current.body.rows).toHaveLength(1);
+    expect(
+      (result.current.body.rows[0] as { original: StudentRow }).original.name,
+    ).toBe('Bob');
+  });
+});
+
 describe('useTanStackTableBuilder onDirectExport', () => {
   beforeEach(() => {
     mockedDownloadFile.mockClear();
diff --git a/client/locales/en.json b/client/locales/en.json
index 2e1646a2018..c985d1e1030 100644
--- a/client/locales/en.json
+++ b/client/locales/en.json
@@ -6289,7 +6289,7 @@
     "defaultMessage": "Student Statistics"
   },
   "course.statistics.StatisticsIndex.students.searchBar": {
-    "defaultMessage": "Search by Student Name or Student Type"
+    "defaultMessage": "Search by Student Name, Student Type or External ID"
   },
   "course.statistics.StatisticsIndex.studentsFailure": {
     "defaultMessage": "Failed to fetch student data!"
@@ -7231,7 +7231,7 @@
     "defaultMessage": "There are no users"
   },
   "course.users.ManageUsersTable.ManageUsersTable.searchText": {
-    "defaultMessage": "Search by name or email"
+    "defaultMessage": "Search by name, email or external ID"
   },
   "course.users.ManageUsersTable.assignToTimeline": {
     "defaultMessage": "Assign to timeline"
diff --git a/client/locales/ko.json b/client/locales/ko.json
index 14d3f6eff9a..4e5335475ca 100644
--- a/client/locales/ko.json
+++ b/client/locales/ko.json
@@ -6270,7 +6270,7 @@
     "defaultMessage": "학생 통계"
   },
   "course.statistics.StatisticsIndex.students.searchBar": {
-    "defaultMessage": "학생 이름 또는 학생 유형으로 검색"
+    "defaultMessage": "학생 이름, 학생 유형 또는 외부 ID로 검색"
   },
   "course.statistics.StatisticsIndex.studentsFailure": {
     "defaultMessage": "학생 데이터를 가져오는 데 실패했습니다!"
@@ -7172,6 +7172,9 @@
   "course.userInvitations.UserInvitationsTable.noInvitations": {
     "defaultMessage": "초대가 없습니다."
   },
+  "course.userInvitations.UserInvitationsTable.searchText": {
+    "defaultMessage": "이름, 이메일 또는 외부 ID로 검색"
+  },
   "course.userInvitations.UserInvitationsTable.pending": {
     "defaultMessage": "대기 중"
   },
@@ -7215,7 +7218,7 @@
     "defaultMessage": "사용자가 없습니다."
   },
   "course.users.ManageUsersTable.ManageUsersTable.searchText": {
-    "defaultMessage": "이름 또는 이메일로 검색"
+    "defaultMessage": "이름, 이메일 또는 외부 ID로 검색"
   },
   "course.users.ManageUsersTable.assignToTimeline": {
     "defaultMessage": "타임라인에 할당"
diff --git a/client/locales/zh.json b/client/locales/zh.json
index 6dac3121633..4595d3f0cb6 100644
--- a/client/locales/zh.json
+++ b/client/locales/zh.json
@@ -6264,7 +6264,7 @@
     "defaultMessage": "学生统计"
   },
   "course.statistics.StatisticsIndex.students.searchBar": {
-    "defaultMessage": "按学生姓名或学生类型搜索"
+    "defaultMessage": "按学生姓名、学生类型或外部编号搜索"
   },
   "course.statistics.StatisticsIndex.studentsFailure": {
     "defaultMessage": "获取学生数据失败！"
@@ -7166,6 +7166,9 @@
   "course.userInvitations.UserInvitationsTable.noInvitations": {
     "defaultMessage": "没有邀请。"
   },
+  "course.userInvitations.UserInvitationsTable.searchText": {
+    "defaultMessage": "按姓名、电子邮件或外部ID搜索"
+  },
   "course.userInvitations.UserInvitationsTable.pending": {
     "defaultMessage": "待处理"
   },
@@ -7209,7 +7212,7 @@
     "defaultMessage": "没有用户"
   },
   "course.users.ManageUsersTable.ManageUsersTable.searchText": {
-    "defaultMessage": "按姓名、电子邮件、角色等搜索。"
+    "defaultMessage": "按姓名、电子邮件或外部ID搜索"
   },
   "course.users.ManageUsersTable.assignToTimeline": {
     "defaultMessage": "分配到时间线"