diff --git chrome/app/chrome_main_delegate.cc chrome/app/chrome_main_delegate.cc
index cc6167f7767ed..c5e33cba1c6d9 100644
--- chrome/app/chrome_main_delegate.cc
+++ chrome/app/chrome_main_delegate.cc
@@ -32,6 +32,7 @@
 #include "base/trace_event/trace_event_impl.h"
 #include "build/build_config.h"
 #include "build/chromeos_buildflags.h"
+#include "cef/libcef/features/runtime.h"
 #include "chrome/browser/chrome_content_browser_client.h"
 #include "chrome/browser/chrome_resource_bundle_helper.h"
 #include "chrome/browser/defaults.h"
@@ -387,6 +388,8 @@ struct MainFunction {
 
 // Initializes the user data dir. Must be called before InitializeLocalState().
 void InitializeUserDataDir(base::CommandLine* command_line) {
+  if (cef::IsChromeRuntimeEnabled())
+    return;
 #if BUILDFLAG(IS_WIN)
   // Reach out to chrome_elf for the truth on the user data directory.
   // Note that in tests, this links to chrome_elf_test_stubs.
@@ -709,7 +712,9 @@ void ChromeMainDelegate::PostFieldTrialInitialization() {
   }
 
 #if BUILDFLAG(IS_WIN)
+  if (!cef::IsChromeRuntimeEnabled()) {
   SetUpExtendedCrashReporting(is_browser_process);
+  }
   base::sequence_manager::internal::ThreadControllerPowerMonitor::
       InitializeOnMainThread();
 #endif
@@ -1022,6 +1027,7 @@ void ChromeMainDelegate::PreSandboxStartup() {
   std::string process_type =
       command_line.GetSwitchValueASCII(switches::kProcessType);
 
+  if (!cef::IsChromeRuntimeEnabled()) {
   crash_reporter::InitializeCrashKeys();
 
 #if BUILDFLAG(IS_POSIX)
@@ -1032,6 +1038,7 @@ void ChromeMainDelegate::PreSandboxStartup() {
   InitMacCrashReporter(command_line, process_type);
   SetUpInstallerPreferences(command_line);
 #endif
+  }  // !cef::IsChromeRuntimeEnabled()
 
 #if BUILDFLAG(IS_WIN)
   child_process_logging::Init();
@@ -1159,6 +1166,7 @@ void ChromeMainDelegate::PreSandboxStartup() {
         locale;
   }
 
+  if (!cef::IsChromeRuntimeEnabled()) {
 #if BUILDFLAG(IS_POSIX) && !BUILDFLAG(IS_MAC)
   // Zygote needs to call InitCrashReporter() in RunZygote().
   if (process_type != switches::kZygoteProcess) {
@@ -1191,6 +1199,7 @@ void ChromeMainDelegate::PreSandboxStartup() {
   // After all the platform Breakpads have been initialized, store the command
   // line for crash reporting.
   crash_keys::SetCrashKeysFromCommandLine(command_line);
+  }  // !cef::IsChromeRuntimeEnabled()
 
 #if BUILDFLAG(ENABLE_PDF)
   MaybePatchGdiGetFontData();
@@ -1276,6 +1285,7 @@ void ChromeMainDelegate::ZygoteForked() {
     SetUpProfilingShutdownHandler();
   }
 
+  if (!cef::IsChromeRuntimeEnabled()) {
   // Needs to be called after we have chrome::DIR_USER_DATA.  BrowserMain sets
   // this up for the browser process in a different manner.
   const base::CommandLine* command_line =
@@ -1292,6 +1302,7 @@ void ChromeMainDelegate::ZygoteForked() {
 
   // Reset the command line for the newly spawned process.
   crash_keys::SetCrashKeysFromCommandLine(*command_line);
+  }  // !cef::IsChromeRuntimeEnabled()
 }
 
 #endif  // BUILDFLAG(IS_LINUX) || BUILDFLAG(IS_CHROMEOS)
diff --git chrome/browser/chrome_browser_main.cc chrome/browser/chrome_browser_main.cc
index 566535f74acf1..4b435553575b0 100644
--- chrome/browser/chrome_browser_main.cc
+++ chrome/browser/chrome_browser_main.cc
@@ -52,6 +52,7 @@
 #include "build/build_config.h"
 #include "build/chromeos_buildflags.h"
 #include "cc/base/switches.h"
+#include "cef/libcef/features/runtime.h"
 #include "chrome/browser/about_flags.h"
 #include "chrome/browser/active_use_util.h"
 #include "chrome/browser/after_startup_task_utils.h"
@@ -1578,11 +1579,13 @@ int ChromeBrowserMainParts::PreMainMessageLoopRunImpl() {
         browser_process_->local_state());
   }
 
+#if !BUILDFLAG(ENABLE_CEF)
   // Needs to be done before PostProfileInit, since login manager on CrOS is
   // called inside PostProfileInit.
   content::WebUIControllerFactory::RegisterFactory(
       ChromeWebUIControllerFactory::GetInstance());
   ChromeUntrustedWebUIControllerFactory::RegisterInstance();
+#endif
 
 #if BUILDFLAG(IS_ANDROID)
   page_info::SetPageInfoClient(new ChromePageInfoClient());
@@ -1745,11 +1748,14 @@ int ChromeBrowserMainParts::PreMainMessageLoopRunImpl() {
   // This step is costly and is already measured in
   // Startup.StartupBrowserCreator_Start.
   // See the comment above for an explanation of |process_command_line|.
+  // Bypass StartupBrowserCreator with CEF where |GetMainRunLoopInstance()| is
+  // nullptr.
   const bool started =
+      !GetMainRunLoopInstance() ||
       !process_command_line ||
       browser_creator_->Start(parsed_command_line(), base::FilePath(),
                               profile_info, last_opened_profiles);
-  if (started) {
+  if (started && GetMainRunLoopInstance()) {
 // TODO(crbug.com/1052397): Revisit the macro expression once build flag switch
 // of lacros-chrome is complete.
 #if BUILDFLAG(IS_WIN) || (BUILDFLAG(IS_LINUX) || BUILDFLAG(IS_CHROMEOS_LACROS))
@@ -1777,8 +1783,10 @@ int ChromeBrowserMainParts::PreMainMessageLoopRunImpl() {
 
     // Create the RunLoop for MainMessageLoopRun() to use and transfer
     // ownership of the browser's lifetime to the BrowserProcess.
+    // CEF with the Chrome runtime will create and manage its own RunLoop.
     DCHECK(!GetMainRunLoopInstance());
-    GetMainRunLoopInstance() = std::make_unique<base::RunLoop>();
+    if (!cef::IsChromeRuntimeEnabled())
+      GetMainRunLoopInstance() = std::make_unique<base::RunLoop>();
     browser_process_->SetQuitClosure(
         GetMainRunLoopInstance()->QuitWhenIdleClosure());
   }
diff --git chrome/browser/chrome_browser_main_mac.mm chrome/browser/chrome_browser_main_mac.mm
index 831d7173873d1..594aee58331a7 100644
--- chrome/browser/chrome_browser_main_mac.mm
+++ chrome/browser/chrome_browser_main_mac.mm
@@ -16,6 +16,7 @@
 #include "base/path_service.h"
 #include "base/strings/sys_string_conversions.h"
 #include "build/branding_buildflags.h"
+#include "cef/libcef/features/features.h"
 #import "chrome/browser/app_controller_mac.h"
 #include "chrome/browser/apps/app_shim/app_shim_listener.h"
 #include "chrome/browser/browser_process.h"
@@ -111,6 +112,7 @@ void ChromeBrowserMainPartsMac::PreCreateMainMessageLoop() {
     }
   }
 
+#if !BUILDFLAG(ENABLE_CEF)
   // Create the app delegate. This object is intentionally leaked as a global
   // singleton. It is accessed through -[NSApp delegate].
   AppController* app_controller = [[AppController alloc] init];
@@ -119,6 +121,7 @@ void ChromeBrowserMainPartsMac::PreCreateMainMessageLoop() {
   chrome::BuildMainMenu(NSApp, app_controller,
                         l10n_util::GetStringUTF16(IDS_PRODUCT_NAME), false);
   [app_controller mainMenuCreated];
+#endif  // BUILDFLAG(ENABLE_CEF)
 
   chrome::DeveloperIDCertificateReauthorizeInApp();
 
@@ -180,7 +183,9 @@ void ChromeBrowserMainPartsMac::PostProfileInit(Profile* profile,
 }
 
 void ChromeBrowserMainPartsMac::DidEndMainMessageLoop() {
+#if !BUILDFLAG(ENABLE_CEF)
   AppController* appController =
       base::mac::ObjCCastStrict<AppController>([NSApp delegate]);
   [appController didEndMainMessageLoop];
+#endif
 }
diff --git chrome/browser/chrome_content_browser_client.cc chrome/browser/chrome_content_browser_client.cc
index 019fd68040dc5..794765646efc7 100644
--- chrome/browser/chrome_content_browser_client.cc
+++ chrome/browser/chrome_content_browser_client.cc
@@ -28,6 +28,7 @@
 #include "base/strings/stringprintf.h"
 #include "build/build_config.h"
 #include "build/chromeos_buildflags.h"
+#include "cef/libcef/features/features.h"
 #include "chrome/browser/accessibility/accessibility_labels_service.h"
 #include "chrome/browser/accessibility/accessibility_labels_service_factory.h"
 #include "chrome/browser/after_startup_task_utils.h"
@@ -1272,6 +1273,8 @@ bool IsTopChromeWebUIURL(const GURL& url) {
 }  // namespace
 
 ChromeContentBrowserClient::ChromeContentBrowserClient() {
+  keepalive_timer_.reset(new base::OneShotTimer());
+
 #if BUILDFLAG(ENABLE_PLUGINS)
   extra_parts_.push_back(new ChromeContentBrowserClientPluginsPart);
 #endif
@@ -1297,6 +1300,11 @@ ChromeContentBrowserClient::~ChromeContentBrowserClient() {
   extra_parts_.clear();
 }
 
+void ChromeContentBrowserClient::CleanupOnUIThread() {
+  DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
+  keepalive_timer_.reset();
+}
+
 // static
 void ChromeContentBrowserClient::RegisterLocalStatePrefs(
     PrefRegistrySimple* registry) {
@@ -3725,9 +3733,11 @@ void ChromeContentBrowserClient::BrowserURLHandlerCreated(
                           &search::HandleNewTabURLReverseRewrite);
 #endif  // BUILDFLAG(IS_ANDROID)
 
+#if !BUILDFLAG(ENABLE_CEF)
   // chrome: & friends.
   handler->AddHandlerPair(&ChromeContentBrowserClient::HandleWebUI,
                           &ChromeContentBrowserClient::HandleWebUIReverse);
+#endif
 }
 
 base::FilePath ChromeContentBrowserClient::GetDefaultDownloadDirectory() {
@@ -5354,7 +5364,7 @@ void ChromeContentBrowserClient::OnNetworkServiceCreated(
       network_service);
 }
 
-void ChromeContentBrowserClient::ConfigureNetworkContextParams(
+bool ChromeContentBrowserClient::ConfigureNetworkContextParams(
     content::BrowserContext* context,
     bool in_memory,
     const base::FilePath& relative_partition_path,
@@ -5372,6 +5382,8 @@ void ChromeContentBrowserClient::ConfigureNetworkContextParams(
     network_context_params->user_agent = GetUserAgentBasedOnPolicy(context);
     network_context_params->accept_language = GetApplicationLocale();
   }
+
+  return true;
 }
 
 std::vector<base::FilePath>
@@ -6212,10 +6224,10 @@ void ChromeContentBrowserClient::OnKeepaliveRequestStarted(
   const auto now = base::TimeTicks::Now();
   const auto timeout = GetKeepaliveTimerTimeout(context);
   keepalive_deadline_ = std::max(keepalive_deadline_, now + timeout);
-  if (keepalive_deadline_ > now && !keepalive_timer_.IsRunning()) {
+  if (keepalive_deadline_ > now && !keepalive_timer_->IsRunning()) {
     DVLOG(1) << "Starting a keepalive timer(" << timeout.InSecondsF()
              << " seconds)";
-    keepalive_timer_.Start(
+    keepalive_timer_->Start(
         FROM_HERE, keepalive_deadline_ - now,
         base::BindOnce(
             &ChromeContentBrowserClient::OnKeepaliveTimerFired,
@@ -6234,7 +6246,8 @@ void ChromeContentBrowserClient::OnKeepaliveRequestFinished() {
   --num_keepalive_requests_;
   if (num_keepalive_requests_ == 0) {
     DVLOG(1) << "Stopping the keepalive timer";
-    keepalive_timer_.Stop();
+    if (keepalive_timer_)
+      keepalive_timer_->Stop();
     // This deletes the keep alive handle attached to the timer function and
     // unblock the shutdown sequence.
   }
@@ -6342,7 +6355,7 @@ void ChromeContentBrowserClient::OnKeepaliveTimerFired(
   const auto now = base::TimeTicks::Now();
   const auto then = keepalive_deadline_;
   if (now < then) {
-    keepalive_timer_.Start(
+    keepalive_timer_->Start(
         FROM_HERE, then - now,
         base::BindOnce(&ChromeContentBrowserClient::OnKeepaliveTimerFired,
                        weak_factory_.GetWeakPtr(),
diff --git chrome/browser/chrome_content_browser_client.h chrome/browser/chrome_content_browser_client.h
index 4aa99834bd6c7..cd932dd3cacf4 100644
--- chrome/browser/chrome_content_browser_client.h
+++ chrome/browser/chrome_content_browser_client.h
@@ -120,6 +120,8 @@ class ChromeContentBrowserClient : public content::ContentBrowserClient {
 
   ~ChromeContentBrowserClient() override;
 
+  virtual void CleanupOnUIThread();
+
   // TODO(https://crbug.com/787567): This file is about calls from content/ out
   // to chrome/ to get values or notify about events, but both of these
   // functions are from chrome/ to chrome/ and don't involve content/ at all.
@@ -561,7 +563,7 @@ class ChromeContentBrowserClient : public content::ContentBrowserClient {
       override;
   void OnNetworkServiceCreated(
       network::mojom::NetworkService* network_service) override;
-  void ConfigureNetworkContextParams(
+  bool ConfigureNetworkContextParams(
       content::BrowserContext* context,
       bool in_memory,
       const base::FilePath& relative_partition_path,
@@ -913,7 +915,7 @@ class ChromeContentBrowserClient : public content::ContentBrowserClient {
 
 #if !BUILDFLAG(IS_ANDROID)
   uint64_t num_keepalive_requests_ = 0;
-  base::OneShotTimer keepalive_timer_;
+  std::unique_ptr<base::OneShotTimer> keepalive_timer_;
   base::TimeTicks keepalive_deadline_;
 #endif
 
diff --git chrome/browser/prefs/browser_prefs.cc chrome/browser/prefs/browser_prefs.cc
index a265ff6d1cf43..cebf6e611c84d 100644
--- chrome/browser/prefs/browser_prefs.cc
+++ chrome/browser/prefs/browser_prefs.cc
@@ -11,6 +11,7 @@
 #include "build/build_config.h"
 #include "build/chromecast_buildflags.h"
 #include "build/chromeos_buildflags.h"
+#include "cef/libcef/features/features.h"
 #include "chrome/browser/about_flags.h"
 #include "chrome/browser/accessibility/accessibility_labels_service.h"
 #include "chrome/browser/accessibility/accessibility_ui.h"
@@ -161,6 +162,10 @@
 #include "chrome/browser/background/background_mode_manager.h"
 #endif
 
+#if BUILDFLAG(ENABLE_CEF)
+#include "cef/libcef/browser/prefs/browser_prefs.h"
+#endif
+
 #if BUILDFLAG(ENABLE_EXTENSIONS)
 #include "chrome/browser/accessibility/animation_policy_prefs.h"
 #include "chrome/browser/apps/platform_apps/shortcut_manager.h"
@@ -1264,6 +1269,10 @@ void RegisterProfilePrefs(user_prefs::PrefRegistrySyncable* registry,
   SessionDataService::RegisterProfilePrefs(registry);
 #endif
 
+#if BUILDFLAG(ENABLE_CEF)
+  browser_prefs::RegisterProfilePrefs(registry);
+#endif
+
 #if BUILDFLAG(ENABLE_EXTENSIONS)
   ExtensionWebUI::RegisterProfilePrefs(registry);
   RegisterAnimationPolicyPrefs(registry);