diff --git a/engine/src/flutter/shell/platform/windows/client_wrapper/flutter_engine.cc b/engine/src/flutter/shell/platform/windows/client_wrapper/flutter_engine.cc
index 63b790bfd7..2287d41d11 100644
--- a/engine/src/flutter/shell/platform/windows/client_wrapper/flutter_engine.cc
+++ b/engine/src/flutter/shell/platform/windows/client_wrapper/flutter_engine.cc
@@ -8,6 +8,7 @@
 #include <iostream>
 
 #include "binary_messenger_impl.h"
+#include "flutter_windows.h"
 
 namespace flutter {
 
@@ -19,8 +20,8 @@ FlutterEngine::FlutterEngine(const DartProject& project) {
   c_engine_properties.dart_entrypoint = project.dart_entrypoint().c_str();
   c_engine_properties.gpu_preference =
       static_cast<FlutterDesktopGpuPreference>(project.gpu_preference());
-  c_engine_properties.merged_platform_ui_thread =
-      project.merged_platform_ui_thread();
+  c_engine_properties.ui_thread_policy =
+      static_cast<FlutterDesktopUIThreadPolicy>(project.ui_thread_policy());
 
   const std::vector<std::string>& entrypoint_args =
       project.dart_entrypoint_arguments();
diff --git a/engine/src/flutter/shell/platform/windows/client_wrapper/include/flutter/dart_project.h b/engine/src/flutter/shell/platform/windows/client_wrapper/include/flutter/dart_project.h
index 3aed8c5eab..8d18146314 100644
--- a/engine/src/flutter/shell/platform/windows/client_wrapper/include/flutter/dart_project.h
+++ b/engine/src/flutter/shell/platform/windows/client_wrapper/include/flutter/dart_project.h
@@ -20,6 +20,17 @@ enum class GpuPreference {
   LowPowerPreference,
 };
 
+// Configures the thread policy for running the UI isolate.
+enum class UIThreadPolicy {
+  // Default value. Currently will run the UI isolate on separate thread,
+  // later will be changed to running the UI isolate on platform thread.
+  Default,
+  // Run the UI isolate on platform thread.
+  RunOnPlatformThread,
+  // Run the UI isolate on a separate thread.
+  RunOnSeparateThread,
+};
+
 // A set of Flutter and Dart assets used to initialize a Flutter engine.
 class DartProject {
  public:
@@ -90,17 +101,14 @@ class DartProject {
   // Defaults to NoPreference.
   GpuPreference gpu_preference() const { return gpu_preference_; }
 
-  // Sets whether the UI isolate should run on the platform thread.
-  // In a future release, this setting will become a no-op when
-  // Flutter Windows requires merged platform and UI threads.
-  void set_merged_platform_ui_thread(bool merged_platform_ui_thread) {
-    merged_platform_ui_thread_ = merged_platform_ui_thread;
+  // Sets the thread policy for UI isolate.
+  void set_ui_thread_policy(UIThreadPolicy policy) {
+    ui_thread_policy_ = policy;
   }
 
-  // Returns whether the UI isolate should run on the platform thread.
-  // Defaults to false. In a future release, this setting will default
-  // to true.
-  bool merged_platform_ui_thread() const { return merged_platform_ui_thread_; }
+  // Returns the policy for UI isolate.
+  // Defaults to UIThreadPolicy::Default.
+  UIThreadPolicy ui_thread_policy() const { return ui_thread_policy_; }
 
  private:
   // Accessors for internals are private, so that they can be changed if more
@@ -128,8 +136,8 @@ class DartProject {
   std::vector<std::string> dart_entrypoint_arguments_;
   // The preference for GPU to be used by flutter engine.
   GpuPreference gpu_preference_ = GpuPreference::NoPreference;
-  // Whether the UI isolate should run on the platform thread.
-  bool merged_platform_ui_thread_ = false;
+  // Thread policy for UI isolate.
+  UIThreadPolicy ui_thread_policy_ = UIThreadPolicy::Default;
 };
 
 }  // namespace flutter
diff --git a/engine/src/flutter/shell/platform/windows/fixtures/main.dart b/engine/src/flutter/shell/platform/windows/fixtures/main.dart
index 5430e86020..f35e9bf356 100644
--- a/engine/src/flutter/shell/platform/windows/fixtures/main.dart
+++ b/engine/src/flutter/shell/platform/windows/fixtures/main.dart
@@ -391,3 +391,8 @@ void onMetricsChangedSignalViewIds() {
 
   signal();
 }
+
+@pragma('vm:entry-point')
+void mergedUIThread() {
+  signal();
+}
diff --git a/engine/src/flutter/shell/platform/windows/flutter_project_bundle.cc b/engine/src/flutter/shell/platform/windows/flutter_project_bundle.cc
index 4971a99776..87cd0b4a32 100644
--- a/engine/src/flutter/shell/platform/windows/flutter_project_bundle.cc
+++ b/engine/src/flutter/shell/platform/windows/flutter_project_bundle.cc
@@ -32,7 +32,8 @@ FlutterProjectBundle::FlutterProjectBundle(
   gpu_preference_ =
       static_cast<FlutterGpuPreference>(properties.gpu_preference);
 
-  merged_platform_ui_thread_ = properties.merged_platform_ui_thread;
+  ui_thread_policy_ =
+      static_cast<FlutterUIThreadPolicy>(properties.ui_thread_policy);
 
   // Resolve any relative paths.
   if (assets_path_.is_relative() || icu_path_.is_relative() ||
diff --git a/engine/src/flutter/shell/platform/windows/flutter_project_bundle.h b/engine/src/flutter/shell/platform/windows/flutter_project_bundle.h
index 34892be3ab..8fa12bc8b9 100644
--- a/engine/src/flutter/shell/platform/windows/flutter_project_bundle.h
+++ b/engine/src/flutter/shell/platform/windows/flutter_project_bundle.h
@@ -22,6 +22,12 @@ enum class FlutterGpuPreference {
   LowPowerPreference,
 };
 
+enum class FlutterUIThreadPolicy {
+  Default,
+  RunOnPlatformThread,
+  RunOnSeparateThread,
+};
+
 // The data associated with a Flutter project needed to run it in an engine.
 class FlutterProjectBundle {
  public:
@@ -67,8 +73,8 @@ class FlutterProjectBundle {
   // Returns the app's GPU preference.
   FlutterGpuPreference gpu_preference() const { return gpu_preference_; }
 
-  // Whether the UI isolate should be running on the platform thread.
-  bool merged_platform_ui_thread() const { return merged_platform_ui_thread_; }
+  // Returns thread policy for running the UI isolate.
+  FlutterUIThreadPolicy ui_thread_policy() { return ui_thread_policy_; }
 
  private:
   std::filesystem::path assets_path_;
@@ -89,8 +95,8 @@ class FlutterProjectBundle {
   // App's GPU preference.
   FlutterGpuPreference gpu_preference_;
 
-  // Whether the UI isolate should be running on the platform thread.
-  bool merged_platform_ui_thread_;
+  // Thread policy for running the UI isolate.
+  FlutterUIThreadPolicy ui_thread_policy_;
 };
 
 }  // namespace flutter
diff --git a/engine/src/flutter/shell/platform/windows/flutter_windows_engine.cc b/engine/src/flutter/shell/platform/windows/flutter_windows_engine.cc
index 6500bd87c8..c78540bcde 100644
--- a/engine/src/flutter/shell/platform/windows/flutter_windows_engine.cc
+++ b/engine/src/flutter/shell/platform/windows/flutter_windows_engine.cc
@@ -26,6 +26,7 @@
 #include "flutter/shell/platform/windows/system_utils.h"
 #include "flutter/shell/platform/windows/task_runner.h"
 #include "flutter/third_party/accessibility/ax/ax_node.h"
+#include "shell/platform/windows/flutter_project_bundle.h"
 
 // winbase.h defines GetCurrentTime as a macro.
 #undef GetCurrentTime
@@ -294,7 +295,8 @@ bool FlutterWindowsEngine::Run(std::string_view entrypoint) {
   custom_task_runners.thread_priority_setter =
       &WindowsPlatformThreadPrioritySetter;
 
-  if (project_->merged_platform_ui_thread()) {
+  if (project_->ui_thread_policy() ==
+      FlutterUIThreadPolicy::RunOnPlatformThread) {
     FML_LOG(WARNING)
         << "Running with merged platform and UI thread. Experimental.";
     custom_task_runners.ui_task_runner = &platform_task_runner;
diff --git a/engine/src/flutter/shell/platform/windows/flutter_windows_engine_unittests.cc b/engine/src/flutter/shell/platform/windows/flutter_windows_engine_unittests.cc
index a7b45f7490..94e8452d4b 100644
--- a/engine/src/flutter/shell/platform/windows/flutter_windows_engine_unittests.cc
+++ b/engine/src/flutter/shell/platform/windows/flutter_windows_engine_unittests.cc
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+#include <thread>
 #include "flutter/shell/platform/windows/flutter_windows_engine.h"
 
 #include "flutter/fml/logging.h"
@@ -27,6 +28,18 @@
 // winbase.h defines GetCurrentTime as a macro.
 #undef GetCurrentTime
 
+namespace {
+// Process the next win32 message if there is one. This can be used to
+// pump the Windows platform thread task runner.
+void PumpMessage() {
+  ::MSG msg;
+  if (::GetMessage(&msg, nullptr, 0, 0)) {
+    ::TranslateMessage(&msg);
+    ::DispatchMessage(&msg);
+  }
+}
+}  // namespace
+
 namespace flutter {
 namespace testing {
 
@@ -1313,5 +1326,25 @@ TEST_F(FlutterWindowsEngineTest, RemoveViewFailureDoesNotHang) {
                      "FlutterEngineRemoveView returned an unexpected result");
 }
 
+TEST_F(FlutterWindowsEngineTest, MergedUIThread) {
+  auto& context = GetContext();
+  WindowsConfigBuilder builder{context};
+  builder.SetDartEntrypoint("mergedUIThread");
+  builder.SetUIThreadPolicy(FlutterDesktopUIThreadPolicy::RunOnPlatformThread);
+
+  std::optional<std::thread::id> ui_thread_id;
+
+  auto native_entry = CREATE_NATIVE_ENTRY([&](Dart_NativeArguments args) {
+    ui_thread_id = std::this_thread::get_id();
+  });
+  context.AddNativeFunction("Signal", native_entry);
+
+  EnginePtr engine{builder.RunHeadless()};
+  while (!ui_thread_id) {
+    PumpMessage();
+  }
+  ASSERT_EQ(*ui_thread_id, std::this_thread::get_id());
+}
+
 }  // namespace testing
 }  // namespace flutter
diff --git a/engine/src/flutter/shell/platform/windows/public/flutter_windows.h b/engine/src/flutter/shell/platform/windows/public/flutter_windows.h
index 6f48798958..5d2bff132b 100644
--- a/engine/src/flutter/shell/platform/windows/public/flutter_windows.h
+++ b/engine/src/flutter/shell/platform/windows/public/flutter_windows.h
@@ -45,6 +45,17 @@ typedef enum {
   LowPowerPreference,
 } FlutterDesktopGpuPreference;
 
+// Configures the thread policy for running the UI isolate.
+typedef enum {
+  // Default value. Currently will run the UI isolate on separate thread,
+  // later will be changed to running the UI isolate on platform thread.
+  Default,
+  // Run the UI isolate on platform thread.
+  RunOnPlatformThread,
+  // Run the UI isolate on a separate thread.
+  RunOnSeparateThread,
+} FlutterDesktopUIThreadPolicy;
+
 // Properties for configuring a Flutter engine instance.
 typedef struct {
   // The path to the flutter_assets folder for the application to be run.
@@ -81,8 +92,8 @@ typedef struct {
   // GPU choice preference
   FlutterDesktopGpuPreference gpu_preference;
 
-  // Whether the UI isolate should run on the platform thread.
-  bool merged_platform_ui_thread;
+  // Policy for the thread that runs UI isolate.
+  FlutterDesktopUIThreadPolicy ui_thread_policy;
 } FlutterDesktopEngineProperties;
 
 // ========== View Controller ==========
diff --git a/engine/src/flutter/shell/platform/windows/testing/windows_test_config_builder.cc b/engine/src/flutter/shell/platform/windows/testing/windows_test_config_builder.cc
index 6456b9add5..96b984cf0b 100644
--- a/engine/src/flutter/shell/platform/windows/testing/windows_test_config_builder.cc
+++ b/engine/src/flutter/shell/platform/windows/testing/windows_test_config_builder.cc
@@ -30,6 +30,11 @@ void WindowsConfigBuilder::SetDartEntrypoint(std::string_view entrypoint) {
   dart_entrypoint_ = entrypoint;
 }
 
+void WindowsConfigBuilder::SetUIThreadPolicy(
+    FlutterDesktopUIThreadPolicy policy) {
+  ui_thread_policy_ = policy;
+}
+
 void WindowsConfigBuilder::AddDartEntrypointArgument(std::string_view arg) {
   if (arg.empty()) {
     return;
@@ -69,6 +74,7 @@ FlutterDesktopEngineProperties WindowsConfigBuilder::GetEngineProperties()
   }
 
   engine_properties.gpu_preference = gpu_preference_;
+  engine_properties.ui_thread_policy = ui_thread_policy_;
 
   return engine_properties;
 }
diff --git a/engine/src/flutter/shell/platform/windows/testing/windows_test_config_builder.h b/engine/src/flutter/shell/platform/windows/testing/windows_test_config_builder.h
index 5cfb87af0b..07da63b245 100644
--- a/engine/src/flutter/shell/platform/windows/testing/windows_test_config_builder.h
+++ b/engine/src/flutter/shell/platform/windows/testing/windows_test_config_builder.h
@@ -58,6 +58,10 @@ class WindowsConfigBuilder {
   // must be decorated with `@pragma('vm:entry-point')`.
   void SetDartEntrypoint(std::string_view entrypoint);
 
+  // Set the UI Thread policy for the engine.
+  // If not set defaults to FlutterDesktopUIThreadPolicy::Default;
+  void SetUIThreadPolicy(FlutterDesktopUIThreadPolicy policy);
+
   // Adds an argument to the Dart entrypoint arguments List<String>.
   void AddDartEntrypointArgument(std::string_view arg);
 
@@ -86,6 +90,8 @@ class WindowsConfigBuilder {
   WindowsTestContext& context_;
   std::string dart_entrypoint_;
   std::vector<std::string> dart_entrypoint_arguments_;
+  FlutterDesktopUIThreadPolicy ui_thread_policy_ =
+      FlutterDesktopUIThreadPolicy::Default;
 
   FlutterDesktopGpuPreference gpu_preference_ =
       FlutterDesktopGpuPreference::NoPreference;