diff --git a/Tests/LibWeb/Text/expected/HTML/shadow-realm-async-evaluate.txt b/Tests/LibWeb/Text/expected/HTML/shadow-realm-async-evaluate.txt
new file mode 100644
index 00000000000..495cc9e1719
--- /dev/null
+++ b/Tests/LibWeb/Text/expected/HTML/shadow-realm-async-evaluate.txt
@@ -0,0 +1 @@
+PASS: Exception thrown 'TypeError: Wrapped value must be primitive or a function object, got [object Promise]'
diff --git a/Tests/LibWeb/Text/expected/HTML/shadow-realm-sync-evaluate.txt b/Tests/LibWeb/Text/expected/HTML/shadow-realm-sync-evaluate.txt
new file mode 100644
index 00000000000..3b0b39fe9bd
--- /dev/null
+++ b/Tests/LibWeb/Text/expected/HTML/shadow-realm-sync-evaluate.txt
@@ -0,0 +1 @@
+Shadow realm evaluation returned: 2
diff --git a/Tests/LibWeb/Text/input/HTML/shadow-realm-async-evaluate.html b/Tests/LibWeb/Text/input/HTML/shadow-realm-async-evaluate.html
new file mode 100644
index 00000000000..46e92a937c4
--- /dev/null
+++ b/Tests/LibWeb/Text/input/HTML/shadow-realm-async-evaluate.html
@@ -0,0 +1,13 @@
+<script src="../include.js"></script>
+<script>
+    test(() => {
+        const realm = new ShadowRealm()
+        const aSync = realm.evaluate(`async () => 1 + 1`);
+        try {
+            aSync();
+            println('Fail! No exception thrown');
+        } catch (e) {
+            println(`PASS: Exception thrown '${e}'`);
+        }
+    })
+</script>
diff --git a/Tests/LibWeb/Text/input/HTML/shadow-realm-sync-evaluate.html b/Tests/LibWeb/Text/input/HTML/shadow-realm-sync-evaluate.html
new file mode 100644
index 00000000000..a1cf3f1fa3d
--- /dev/null
+++ b/Tests/LibWeb/Text/input/HTML/shadow-realm-sync-evaluate.html
@@ -0,0 +1,8 @@
+<script src="../include.js"></script>
+<script>
+    test(() => {
+        const realm = new ShadowRealm();
+        const result = realm.evaluate(`() => 1 + 1`)();
+        println(`Shadow realm evaluation returned: ${result}`);
+    });
+</script>
diff --git a/Userland/Libraries/LibJS/Runtime/Realm.h b/Userland/Libraries/LibJS/Runtime/Realm.h
index a47eff87519..d09c5cfc30b 100644
--- a/Userland/Libraries/LibJS/Runtime/Realm.h
+++ b/Userland/Libraries/LibJS/Runtime/Realm.h
@@ -34,7 +34,10 @@ public:
     static ThrowCompletionOr<NonnullOwnPtr<ExecutionContext>> initialize_host_defined_realm(VM&, Function<Object*(Realm&)> create_global_object, Function<Object*(Realm&)> create_global_this_value);
 
     [[nodiscard]] Object& global_object() const { return *m_global_object; }
+    void set_global_object(NonnullGCPtr<Object> global) { m_global_object = global; }
+
     [[nodiscard]] GlobalEnvironment& global_environment() const { return *m_global_environment; }
+    void set_global_environment(NonnullGCPtr<GlobalEnvironment> environment) { m_global_environment = environment; }
 
     [[nodiscard]] Intrinsics const& intrinsics() const { return *m_intrinsics; }
     [[nodiscard]] Intrinsics& intrinsics() { return *m_intrinsics; }
diff --git a/Userland/Libraries/LibWeb/Bindings/MainThreadVM.cpp b/Userland/Libraries/LibWeb/Bindings/MainThreadVM.cpp
index d561e1f66db..5d3a54d7e41 100644
--- a/Userland/Libraries/LibWeb/Bindings/MainThreadVM.cpp
+++ b/Userland/Libraries/LibWeb/Bindings/MainThreadVM.cpp
@@ -13,13 +13,16 @@
 #include <LibJS/Runtime/Array.h>
 #include <LibJS/Runtime/Environment.h>
 #include <LibJS/Runtime/FinalizationRegistry.h>
+#include <LibJS/Runtime/GlobalEnvironment.h>
 #include <LibJS/Runtime/ModuleRequest.h>
 #include <LibJS/Runtime/NativeFunction.h>
+#include <LibJS/Runtime/ShadowRealm.h>
 #include <LibJS/Runtime/VM.h>
 #include <LibJS/SourceTextModule.h>
 #include <LibWeb/Bindings/ExceptionOrUtils.h>
 #include <LibWeb/Bindings/Intrinsics.h>
 #include <LibWeb/Bindings/MainThreadVM.h>
+#include <LibWeb/Bindings/SyntheticHostDefined.h>
 #include <LibWeb/Bindings/WindowExposedInterfaces.h>
 #include <LibWeb/DOM/Document.h>
 #include <LibWeb/DOM/MutationType.h>
@@ -35,7 +38,9 @@
 #include <LibWeb/HTML/Scripting/Fetching.h>
 #include <LibWeb/HTML/Scripting/ModuleScript.h>
 #include <LibWeb/HTML/Scripting/Script.h>
+#include <LibWeb/HTML/Scripting/SyntheticRealmSettings.h>
 #include <LibWeb/HTML/Scripting/TemporaryExecutionContext.h>
+#include <LibWeb/HTML/ShadowRealmGlobalScope.h>
 #include <LibWeb/HTML/TagNames.h>
 #include <LibWeb/HTML/Window.h>
 #include <LibWeb/HTML/WindowProxy.h>
@@ -560,6 +565,45 @@ ErrorOr<void> initialize_main_thread_vm(HTML::EventLoop::Type type)
         HTML::fetch_single_imported_module_script(*module_map_realm, url.release_value(), *fetch_client, destination, fetch_options, *module_map_realm, fetch_referrer, module_request, perform_fetch, on_single_fetch_complete);
     };
 
+    // https://whatpr.org/html/9893/webappapis.html#hostinitializeshadowrealm(realm,-context,-o)
+    // 8.1.6.8 HostInitializeShadowRealm(realm, context, O)
+    s_main_thread_vm->host_initialize_shadow_realm = [](JS::Realm& realm, NonnullOwnPtr<JS::ExecutionContext> context, JS::ShadowRealm& object) -> JS::ThrowCompletionOr<void> {
+        // FIXME: 1. Set realm's is global prototype chain mutable to true.
+
+        // 2. Let globalObject be a new ShadowRealmGlobalScope object with realm.
+        auto global_object = HTML::ShadowRealmGlobalScope::create(realm);
+
+        // 3. Let settings be a new synthetic realm settings object that this algorithm will subsequently initialize.
+        auto settings = HTML::SyntheticRealmSettings {
+            // 4. Set settings's execution context to context.
+            .execution_context = move(context),
+
+            // 5. Set settings's principal realm to O's associated realm
+            .principal_realm = object.shape().realm(),
+
+            // 6. Set settings's underlying realm to realm.
+            .underlying_realm = realm,
+
+            // 7. Set settings's module map to a new module map, initially empty.
+            .module_map = realm.heap().allocate<HTML::ModuleMap>(realm),
+        };
+
+        // 8. Set realm.[[HostDefined]] to settings.
+        realm.set_host_defined(make<Bindings::SyntheticHostDefined>(move(settings)));
+
+        // 9. Set realm.[[GlobalObject]] to globalObject.
+        realm.set_global_object(global_object);
+
+        // 10. Set realm.[[GlobalEnv]] to NewGlobalEnvironment(globalObject, globalObject).
+        realm.set_global_environment(realm.vm().heap().allocate_without_realm<JS::GlobalEnvironment>(global_object, global_object));
+
+        // 11. Perform ? SetDefaultGlobalBindings(realm).
+        set_default_global_bindings(realm);
+
+        // 12. Return NormalCompletion(unused).
+        return {};
+    };
+
     s_main_thread_vm->host_unrecognized_date_string = [](StringView date) {
         dbgln("Unable to parse date string: \"{}\"", date);
     };