diff --git a/.changeset/eager-wolves-enjoy.md b/.changeset/eager-wolves-enjoy.md
new file mode 100644
index 0000000000..7807cfafd2
--- /dev/null
+++ b/.changeset/eager-wolves-enjoy.md
@@ -0,0 +1,5 @@
+---
+'@backstage/frontend-test-utils': patch
+---
+
+Added support for `ExternalRouteRef` in the `mountedRoutes` option of `renderInTestApp` and `renderTestApp`.
diff --git a/packages/frontend-test-utils/report.api.md b/packages/frontend-test-utils/report.api.md
index 6d9f8964b1..d24046953f 100644
--- a/packages/frontend-test-utils/report.api.md
+++ b/packages/frontend-test-utils/report.api.md
@@ -26,6 +26,7 @@ import { EvaluatePermissionResponse } from '@backstage/plugin-permission-common'
 import { ExtensionDataRef } from '@backstage/frontend-plugin-api';
 import { ExtensionDefinition } from '@backstage/frontend-plugin-api';
 import { ExtensionDefinitionParameters } from '@backstage/frontend-plugin-api';
+import { ExternalRouteRef } from '@backstage/frontend-plugin-api';
 import { FeatureFlag } from '@backstage/frontend-plugin-api';
 import { FeatureFlagsApi } from '@backstage/frontend-plugin-api';
 import { FeatureFlagsSaveOptions } from '@backstage/frontend-plugin-api';
@@ -444,7 +445,7 @@ export type RenderTestAppOptions<TApiPairs extends any[] = any[]> = {
   features?: FrontendFeature[];
   initialRouteEntries?: string[];
   mountedRoutes?: {
-    [path: string]: RouteRef;
+    [path: string]: RouteRef | ExternalRouteRef;
   };
   apis?: readonly [...TestApiPairs<TApiPairs>];
 };
@@ -473,7 +474,7 @@ export type TestApiProviderProps<TApiPairs extends any[]> = {
 // @public
 export type TestAppOptions<TApiPairs extends any[] = any[]> = {
   mountedRoutes?: {
-    [path: string]: RouteRef;
+    [path: string]: RouteRef | ExternalRouteRef;
   };
   config?: JsonObject;
   features?: FrontendFeature[];
diff --git a/packages/frontend-test-utils/src/app/renderInTestApp.test.tsx b/packages/frontend-test-utils/src/app/renderInTestApp.test.tsx
index c9d90715f6..aa3236be86 100644
--- a/packages/frontend-test-utils/src/app/renderInTestApp.test.tsx
+++ b/packages/frontend-test-utils/src/app/renderInTestApp.test.tsx
@@ -17,7 +17,12 @@
 import { useCallback } from 'react';
 import { screen, fireEvent } from '@testing-library/react';
 import { mockApis, TestApiProvider } from '@backstage/frontend-test-utils';
-import { useAnalytics } from '@backstage/frontend-plugin-api';
+import {
+  useAnalytics,
+  createRouteRef,
+  createExternalRouteRef,
+  useRouteRef,
+} from '@backstage/frontend-plugin-api';
 import { Routes, Route } from 'react-router-dom';
 import { renderInTestApp } from './renderInTestApp';
 
@@ -108,4 +113,40 @@ describe('renderInTestApp', () => {
       ]),
     );
   });
+
+  it('should allow mounting route refs', () => {
+    const testRouteRef = createRouteRef({
+      params: ['name'],
+    });
+
+    const LinkComponent = () => {
+      const link = useRouteRef(testRouteRef);
+      return <div>Link: {link?.({ name: 'test-name' }) ?? 'none'}</div>;
+    };
+
+    renderInTestApp(<LinkComponent />, {
+      mountedRoutes: {
+        '/test-path/:name': testRouteRef,
+      },
+    });
+
+    expect(screen.getByText('Link: /test-path/test-name')).toBeInTheDocument();
+  });
+
+  it('should allow mounting external route refs', () => {
+    const externalRef = createExternalRouteRef({ params: ['name'] });
+
+    const ExternalLinkComponent = () => {
+      const link = useRouteRef(externalRef);
+      return <div>Link: {link?.({ name: 'test' }) ?? 'none'}</div>;
+    };
+
+    renderInTestApp(<ExternalLinkComponent />, {
+      mountedRoutes: {
+        '/items/:name': externalRef,
+      },
+    });
+
+    expect(screen.getByText('Link: /items/test')).toBeInTheDocument();
+  });
 });
diff --git a/packages/frontend-test-utils/src/app/renderInTestApp.tsx b/packages/frontend-test-utils/src/app/renderInTestApp.tsx
index bdb9929635..935e479f9c 100644
--- a/packages/frontend-test-utils/src/app/renderInTestApp.tsx
+++ b/packages/frontend-test-utils/src/app/renderInTestApp.tsx
@@ -32,6 +32,8 @@ import {
   FrontendFeature,
   createFrontendModule,
   createApiFactory,
+  createRouteRef,
+  ExternalRouteRef,
   type ApiRef,
 } from '@backstage/frontend-plugin-api';
 import { RouterBlueprint } from '@backstage/plugin-app-react';
@@ -40,6 +42,7 @@ import { getMockApiFactory } from '../apis/MockWithApiFactory';
 // eslint-disable-next-line @backstage/no-relative-monorepo-imports
 import type { CreateSpecializedAppInternalOptions } from '../../../frontend-app-api/src/wiring/createSpecializedApp';
 import { TestApiPairs } from '../apis/TestApiProvider';
+import { OpaqueExternalRouteRef } from '@internal/frontend';
 
 const DEFAULT_MOCK_CONFIG = {
   app: { baseUrl: 'http://localhost:3000' },
@@ -67,7 +70,7 @@ export type TestAppOptions<TApiPairs extends any[] = any[]> = {
    * const link = useRouteRef(myRouteRef)
    * ```
    */
-  mountedRoutes?: { [path: string]: RouteRef };
+  mountedRoutes?: { [path: string]: RouteRef | ExternalRouteRef };
 
   /**
    * Additional configuration passed to the app when rendering elements inside it.
@@ -180,9 +183,20 @@ export function renderInTestApp<const TApiPairs extends any[] = any[]>(
     }),
   ];
 
+  const externalBindings = new Map<ExternalRouteRef, RouteRef>();
+
   if (options?.mountedRoutes) {
-    for (const [path, routeRef] of Object.entries(options.mountedRoutes)) {
-      // TODO(Rugvip): add support for external route refs
+    for (const [path, optionRef] of Object.entries(options.mountedRoutes)) {
+      let routeRef: RouteRef;
+
+      if (OpaqueExternalRouteRef.isType(optionRef)) {
+        // Create an actual route ref for the external route, then bind the external ref to it
+        routeRef = createRouteRef();
+        externalBindings.set(optionRef, routeRef);
+      } else {
+        routeRef = optionRef;
+      }
+
       extensions.push(
         createExtension({
           kind: 'test-route',
@@ -253,6 +267,14 @@ export function renderInTestApp<const TApiPairs extends any[] = any[]>(
         return createApiFactory(apiRef, implementation);
       }),
     },
+    bindRoutes:
+      externalBindings.size > 0
+        ? ({ bind }) => {
+            for (const [externalRef, targetRef] of externalBindings) {
+              bind({ ref: externalRef }, { ref: targetRef });
+            }
+          }
+        : undefined,
   } as CreateSpecializedAppInternalOptions).finalize();
 
   return render(
diff --git a/packages/frontend-test-utils/src/app/renderTestApp.tsx b/packages/frontend-test-utils/src/app/renderTestApp.tsx
index 7708fa4220..d459f29ac1 100644
--- a/packages/frontend-test-utils/src/app/renderTestApp.tsx
+++ b/packages/frontend-test-utils/src/app/renderTestApp.tsx
@@ -25,6 +25,8 @@ import {
   ExtensionDefinition,
   FrontendFeature,
   RouteRef,
+  ExternalRouteRef,
+  createRouteRef,
   type ApiRef,
 } from '@backstage/frontend-plugin-api';
 import { render, type RenderResult } from '@testing-library/react';
@@ -37,6 +39,7 @@ import { getMockApiFactory } from '../apis/MockWithApiFactory';
 // eslint-disable-next-line @backstage/no-relative-monorepo-imports
 import type { CreateSpecializedAppInternalOptions } from '../../../frontend-app-api/src/wiring/createSpecializedApp';
 import { TestApiPairs } from '../apis/TestApiProvider';
+import { OpaqueExternalRouteRef } from '@internal/frontend';
 
 const DEFAULT_MOCK_CONFIG = {
   app: { baseUrl: 'http://localhost:3000' },
@@ -83,7 +86,7 @@ export type RenderTestAppOptions<TApiPairs extends any[] = any[]> = {
    * })
    * ```
    */
-  mountedRoutes?: { [path: string]: RouteRef };
+  mountedRoutes?: { [path: string]: RouteRef | ExternalRouteRef };
 
   /**
    * API overrides to provide to the test app. Use `mockApis` helpers
@@ -121,8 +124,20 @@ export function renderTestApp<const TApiPairs extends any[] = any[]>(
 ): RenderResult {
   const extensions = [...(options?.extensions ?? [])];
 
+  const externalBindings = new Map<ExternalRouteRef, RouteRef>();
+
   if (options?.mountedRoutes) {
-    for (const [path, routeRef] of Object.entries(options.mountedRoutes)) {
+    for (const [path, optionRef] of Object.entries(options.mountedRoutes)) {
+      let routeRef: RouteRef;
+
+      if (OpaqueExternalRouteRef.isType(optionRef)) {
+        // Create an actual route ref for the external route, then bind the external ref to it
+        routeRef = createRouteRef();
+        externalBindings.set(optionRef, routeRef);
+      } else {
+        routeRef = optionRef;
+      }
+
       extensions.push(
         createExtension({
           kind: 'test-route',
@@ -193,6 +208,14 @@ export function renderTestApp<const TApiPairs extends any[] = any[]>(
         return createApiFactory(apiRef, implementation);
       }),
     },
+    bindRoutes:
+      externalBindings.size > 0
+        ? ({ bind }) => {
+            for (const [externalRef, targetRef] of externalBindings) {
+              bind({ ref: externalRef }, { ref: targetRef });
+            }
+          }
+        : undefined,
   } as CreateSpecializedAppInternalOptions).finalize();
 
   return render(