diff --git a/src/material-experimental/mdc-dialog/BUILD.bazel b/src/material-experimental/mdc-dialog/BUILD.bazel
index 432a6c8cab28..12a65f47ac2b 100644
--- a/src/material-experimental/mdc-dialog/BUILD.bazel
+++ b/src/material-experimental/mdc-dialog/BUILD.bazel
@@ -65,6 +65,7 @@ ng_test_library(
         "//src/cdk/bidi",
         "//src/cdk/keycodes",
         "//src/cdk/overlay",
+        "//src/cdk/platform",
         "//src/cdk/scrolling",
         "//src/cdk/testing/private",
         "@npm//@angular/common",
diff --git a/src/material-experimental/mdc-dialog/dialog.spec.ts b/src/material-experimental/mdc-dialog/dialog.spec.ts
index 551997ffbb8a..cfde5a9011a7 100644
--- a/src/material-experimental/mdc-dialog/dialog.spec.ts
+++ b/src/material-experimental/mdc-dialog/dialog.spec.ts
@@ -2,6 +2,7 @@ import {FocusMonitor, FocusOrigin} from '@angular/cdk/a11y';
 import {Directionality} from '@angular/cdk/bidi';
 import {A, ESCAPE} from '@angular/cdk/keycodes';
 import {Overlay, OverlayContainer, ScrollStrategy} from '@angular/cdk/overlay';
+import {_supportsShadowDom} from '@angular/cdk/platform';
 import {ScrollDispatcher} from '@angular/cdk/scrolling';
 import {
   createKeyboardEvent,
@@ -23,7 +24,8 @@ import {
   NgZone,
   TemplateRef,
   ViewChild,
-  ViewContainerRef
+  ViewContainerRef,
+  ViewEncapsulation
 } from '@angular/core';
 import {
   ComponentFixture,
@@ -34,6 +36,7 @@ import {
   TestBed,
   tick,
 } from '@angular/core/testing';
+import {By} from '@angular/platform-browser';
 import {BrowserAnimationsModule, NoopAnimationsModule} from '@angular/platform-browser/animations';
 import {numbers} from '@material/dialog';
 import {Subject} from 'rxjs';
@@ -1075,6 +1078,32 @@ describe('MDC-based MatDialog', () => {
          document.body.removeChild(button);
        }));
 
+    it('should re-focus trigger element inside the shadow DOM when dialog closes', fakeAsync(() => {
+      if (!_supportsShadowDom()) {
+        return;
+      }
+
+      viewContainerFixture.destroy();
+      const fixture = TestBed.createComponent(ShadowDomComponent);
+      fixture.detectChanges();
+      const button = fixture.debugElement.query(By.css('button'))!.nativeElement;
+
+      button.focus();
+
+      const dialogRef = dialog.open(PizzaMsg);
+      flushMicrotasks();
+      fixture.detectChanges();
+      flushMicrotasks();
+
+      const spy = spyOn(button, 'focus').and.callThrough();
+      dialogRef.close();
+      flushMicrotasks();
+      fixture.detectChanges();
+      tick(500);
+
+      expect(spy).toHaveBeenCalled();
+    }));
+
     it('should re-focus the trigger via keyboard when closed via escape key', fakeAsync(() => {
          const button = document.createElement('button');
          let lastFocusOrigin: FocusOrigin = null;
@@ -1870,6 +1899,12 @@ class DialogWithInjectedData {
 class DialogWithoutFocusableElements {
 }
 
+@Component({
+  template: `<button>I'm a button</button>`,
+  encapsulation: ViewEncapsulation.ShadowDom
+})
+class ShadowDomComponent {}
+
 // Create a real (non-test) NgModule as a workaround for
 // https://github.com/angular/angular/issues/10760
 const TEST_DIRECTIVES = [
@@ -1882,6 +1917,7 @@ const TEST_DIRECTIVES = [
   DialogWithInjectedData,
   DialogWithoutFocusableElements,
   ComponentWithContentElementTemplateRef,
+  ShadowDomComponent,
 ];
 
 @NgModule({
diff --git a/src/material/dialog/BUILD.bazel b/src/material/dialog/BUILD.bazel
index a13a3df9f276..2c9a4e88d846 100644
--- a/src/material/dialog/BUILD.bazel
+++ b/src/material/dialog/BUILD.bazel
@@ -61,6 +61,7 @@ ng_test_library(
         "//src/cdk/bidi",
         "//src/cdk/keycodes",
         "//src/cdk/overlay",
+        "//src/cdk/platform",
         "//src/cdk/scrolling",
         "//src/cdk/testing/private",
         "@npm//@angular/common",
diff --git a/src/material/dialog/dialog-container.ts b/src/material/dialog/dialog-container.ts
index 10dbe5c40bb0..32088f65589e 100644
--- a/src/material/dialog/dialog-container.ts
+++ b/src/material/dialog/dialog-container.ts
@@ -182,7 +182,7 @@ export abstract class _MatDialogContainerBase extends BasePortalOutlet {
     // We need the extra check, because IE can set the `activeElement` to null in some cases.
     if (this._config.restoreFocus && previousElement &&
         typeof previousElement.focus === 'function') {
-      const activeElement = this._document.activeElement;
+      const activeElement = this._getActiveElement();
       const element = this._elementRef.nativeElement;
 
       // Make sure that focus is still inside the dialog or is on the body (usually because a
@@ -213,7 +213,7 @@ export abstract class _MatDialogContainerBase extends BasePortalOutlet {
   /** Captures the element that was focused before the dialog was opened. */
   private _capturePreviouslyFocusedElement() {
     if (this._document) {
-      this._elementFocusedBeforeDialogWasOpened = this._document.activeElement as HTMLElement;
+      this._elementFocusedBeforeDialogWasOpened = this._getActiveElement() as HTMLElement;
     }
   }
 
@@ -228,9 +228,17 @@ export abstract class _MatDialogContainerBase extends BasePortalOutlet {
   /** Returns whether focus is inside the dialog. */
   private _containsFocus() {
     const element = this._elementRef.nativeElement;
-    const activeElement = this._document.activeElement;
+    const activeElement = this._getActiveElement();
     return element === activeElement || element.contains(activeElement);
   }
+
+  /** Gets the currently-focused element on the page. */
+  private _getActiveElement(): Element | null {
+    // If the `activeElement` is inside a shadow root, `document.activeElement` will
+    // point to the shadow root so we have to descend into it ourselves.
+    const activeElement = this._document.activeElement;
+    return activeElement?.shadowRoot?.activeElement as HTMLElement || activeElement;
+  }
 }
 
 /**
diff --git a/src/material/dialog/dialog.spec.ts b/src/material/dialog/dialog.spec.ts
index 307d4b2b6184..687e31d70ac5 100644
--- a/src/material/dialog/dialog.spec.ts
+++ b/src/material/dialog/dialog.spec.ts
@@ -19,13 +19,15 @@ import {
   ViewChild,
   ViewContainerRef,
   ComponentFactoryResolver,
-  NgZone
+  NgZone,
+  ViewEncapsulation
 } from '@angular/core';
 import {By} from '@angular/platform-browser';
 import {BrowserAnimationsModule, NoopAnimationsModule} from '@angular/platform-browser/animations';
 import {Location} from '@angular/common';
 import {SpyLocation} from '@angular/common/testing';
 import {Directionality} from '@angular/cdk/bidi';
+import {_supportsShadowDom} from '@angular/cdk/platform';
 import {MatDialogContainer} from './dialog-container';
 import {OverlayContainer, ScrollStrategy, Overlay} from '@angular/cdk/overlay';
 import {ScrollDispatcher} from '@angular/cdk/scrolling';
@@ -1166,6 +1168,32 @@ describe('MatDialog', () => {
       document.body.removeChild(button);
     }));
 
+    it('should re-focus trigger element inside the shadow DOM when dialog closes', fakeAsync(() => {
+      if (!_supportsShadowDom()) {
+        return;
+      }
+
+      viewContainerFixture.destroy();
+      const fixture = TestBed.createComponent(ShadowDomComponent);
+      fixture.detectChanges();
+      const button = fixture.debugElement.query(By.css('button'))!.nativeElement;
+
+      button.focus();
+
+      const dialogRef = dialog.open(PizzaMsg);
+      flushMicrotasks();
+      fixture.detectChanges();
+      flushMicrotasks();
+
+      const spy = spyOn(button, 'focus').and.callThrough();
+      dialogRef.close();
+      flushMicrotasks();
+      fixture.detectChanges();
+      tick(500);
+
+      expect(spy).toHaveBeenCalled();
+    }));
+
     it('should re-focus the trigger via keyboard when closed via escape key', fakeAsync(() => {
       const button = document.createElement('button');
       let lastFocusOrigin: FocusOrigin = null;
@@ -1947,6 +1975,12 @@ class DialogWithInjectedData {
 @Component({template: '<p>Pasta</p>'})
 class DialogWithoutFocusableElements {}
 
+@Component({
+  template: `<button>I'm a button</button>`,
+  encapsulation: ViewEncapsulation.ShadowDom
+})
+class ShadowDomComponent {}
+
 // Create a real (non-test) NgModule as a workaround for
 // https://github.com/angular/angular/issues/10760
 const TEST_DIRECTIVES = [
@@ -1959,6 +1993,7 @@ const TEST_DIRECTIVES = [
   DialogWithInjectedData,
   DialogWithoutFocusableElements,
   ComponentWithContentElementTemplateRef,
+  ShadowDomComponent,
 ];
 
 @NgModule({