diff --git a/packages/language-service/src/ts_plugin.ts b/packages/language-service/src/ts_plugin.ts
index d0a3a5005f870..05ad3c79c1936 100644
--- a/packages/language-service/src/ts_plugin.ts
+++ b/packages/language-service/src/ts_plugin.ts
@@ -11,8 +11,30 @@ import * as tss from 'typescript/lib/tsserverlibrary';
 import {createLanguageService} from './language_service';
 import {TypeScriptServiceHost} from './typescript_host';
 
+// Use a WeakMap to keep track of Project to Host mapping so that when Project
+// is deleted Host could be garbage collected.
+const PROJECT_MAP = new WeakMap<tss.server.Project, TypeScriptServiceHost>();
+
+/**
+ * This function is called by tsserver to retrieve the external (non-TS) files
+ * that should belong to the specified `project`. For Angular, these files are
+ * external templates. This is called once when the project is loaded, then
+ * every time when the program is updated.
+ * @param project Project for which external files should be retrieved.
+ */
+export function getExternalFiles(project: tss.server.Project): string[] {
+  if (!project.hasRoots()) {
+    // During project initialization where there is no root files yet we should
+    // not do any work.
+    return [];
+  }
+  const ngLsHost = PROJECT_MAP.get(project);
+  ngLsHost?.getAnalyzedModules();
+  return ngLsHost?.getExternalTemplates() || [];
+}
+
 export function create(info: tss.server.PluginCreateInfo): tss.LanguageService {
-  const {languageService: tsLS, languageServiceHost: tsLSHost, config} = info;
+  const {languageService: tsLS, languageServiceHost: tsLSHost, config, project} = info;
   // This plugin could operate under two different modes:
   // 1. TS + Angular
   //    Plugin augments TS language service to provide additional Angular
@@ -25,6 +47,7 @@ export function create(info: tss.server.PluginCreateInfo): tss.LanguageService {
   const angularOnly = config ? config.angularOnly === true : false;
   const ngLSHost = new TypeScriptServiceHost(tsLSHost, tsLS);
   const ngLS = createLanguageService(ngLSHost);
+  PROJECT_MAP.set(project, ngLSHost);
 
   function getCompletionsAtPosition(
       fileName: string, position: number, options: tss.GetCompletionsAtPositionOptions|undefined) {
diff --git a/packages/language-service/src/typescript_host.ts b/packages/language-service/src/typescript_host.ts
index cf4bf437b0506..ae927fd77d66e 100644
--- a/packages/language-service/src/typescript_host.ts
+++ b/packages/language-service/src/typescript_host.ts
@@ -151,6 +151,13 @@ export class TypeScriptServiceHost implements LanguageServiceHost {
     return this.resolver.getReflector() as StaticReflector;
   }
 
+  /**
+   * Return all known external templates.
+   */
+  getExternalTemplates(): string[] {
+    return [...this.fileToComponent.keys()];
+  }
+
   /**
    * Checks whether the program has changed and returns all analyzed modules.
    * If program has changed, invalidate all caches and update fileToComponent
diff --git a/packages/language-service/test/ts_plugin_spec.ts b/packages/language-service/test/ts_plugin_spec.ts
index eecf10125741e..dc82a9cf58523 100644
--- a/packages/language-service/test/ts_plugin_spec.ts
+++ b/packages/language-service/test/ts_plugin_spec.ts
@@ -8,7 +8,7 @@
 
 import * as ts from 'typescript';
 
-import {create} from '../src/ts_plugin';
+import {create, getExternalFiles} from '../src/ts_plugin';
 import {CompletionKind} from '../src/types';
 
 import {MockTypescriptHost} from './test_utils';
@@ -129,6 +129,13 @@ describe('plugin', () => {
       },
     ]);
   });
+
+  it('should return external templates when getExternalFiles() is called', () => {
+    const externalTemplates = getExternalFiles(mockProject);
+    expect(externalTemplates).toEqual([
+      '/app/test.ng',
+    ]);
+  });
 });
 
 describe(`with config 'angularOnly = true`, () => {