diff --git chrome/app/chrome_main_delegate.cc chrome/app/chrome_main_delegate.cc
index 132735e3a1200..0d392976799a4 100644
--- chrome/app/chrome_main_delegate.cc
+++ chrome/app/chrome_main_delegate.cc
@@ -31,6 +31,7 @@
 #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"
@@ -390,6 +391,8 @@ 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.
@@ -712,7 +715,9 @@ void ChromeMainDelegate::PostFieldTrialInitialization() {
   }
 
 #if BUILDFLAG(IS_WIN)
+  if (!cef::IsChromeRuntimeEnabled()) {
   SetUpExtendedCrashReporting(is_browser_process);
+  }
   base::sequence_manager::internal::ThreadControllerPowerMonitor::
       InitializeOnMainThread();
 #endif
@@ -1010,6 +1015,7 @@ void ChromeMainDelegate::PreSandboxStartup() {
   std::string process_type =
       command_line.GetSwitchValueASCII(switches::kProcessType);
 
+  if (!cef::IsChromeRuntimeEnabled()) {
   crash_reporter::InitializeCrashKeys();
 
 #if BUILDFLAG(IS_POSIX)
@@ -1020,6 +1026,7 @@ void ChromeMainDelegate::PreSandboxStartup() {
   InitMacCrashReporter(command_line, process_type);
   SetUpInstallerPreferences(command_line);
 #endif
+  }  // !cef::IsChromeRuntimeEnabled()
 
 #if BUILDFLAG(IS_WIN)
   child_process_logging::Init();
@@ -1146,6 +1153,7 @@ 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) {
@@ -1178,6 +1186,7 @@ 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();
@@ -1269,6 +1278,7 @@ 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 =
@@ -1285,6 +1295,7 @@ 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 4e9969d9c5b0b..e599b114f021d 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"
@@ -1530,11 +1531,13 @@ 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());
@@ -1757,11 +1760,14 @@ 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))
@@ -1789,8 +1795,10 @@ 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 dbd8f7ebe071d..b0f8d3d7bcff9 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"
@@ -110,6 +111,7 @@ 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];
@@ -118,6 +120,7 @@ void ChromeBrowserMainPartsMac::PreCreateMainMessageLoop() {
   chrome::BuildMainMenu(NSApp, app_controller,
                         l10n_util::GetStringUTF16(IDS_PRODUCT_NAME), false);
   [app_controller mainMenuCreated];
+#endif  // BUILDFLAG(ENABLE_CEF)
 
   PrefService* local_state = g_browser_process->local_state();
   DCHECK(local_state);
@@ -177,7 +180,9 @@ 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 70df7bef3a7b1..97d130a0a1be6 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"
@@ -3682,9 +3683,11 @@ 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() {
@@ -5333,7 +5336,7 @@ void ChromeContentBrowserClient::OnNetworkServiceCreated(
       network_service);
 }
 
-void ChromeContentBrowserClient::ConfigureNetworkContextParams(
+bool ChromeContentBrowserClient::ConfigureNetworkContextParams(
     content::BrowserContext* context,
     bool in_memory,
     const base::FilePath& relative_partition_path,
@@ -5351,6 +5354,8 @@ void ChromeContentBrowserClient::ConfigureNetworkContextParams(
     network_context_params->user_agent = GetUserAgentBasedOnPolicy(context);
     network_context_params->accept_language = GetApplicationLocale();
   }
+
+  return true;
 }
 
 std::vector<base::FilePath>
diff --git chrome/browser/chrome_content_browser_client.h chrome/browser/chrome_content_browser_client.h
index 71dfd396b405e..879210ff7c8fd 100644
--- chrome/browser/chrome_content_browser_client.h
+++ chrome/browser/chrome_content_browser_client.h
@@ -549,7 +549,7 @@ 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,
diff --git chrome/browser/prefs/browser_prefs.cc chrome/browser/prefs/browser_prefs.cc
index 3ae5f0a699de3..d66d193121be5 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"
@@ -164,6 +165,10 @@
 #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"
@@ -1267,6 +1272,10 @@ 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);