diff --git a/shell/browser/api/electron_api_app.cc b/shell/browser/api/electron_api_app.cc
index 540ee1e0b3395..2ba1e0adbe872 100644
--- a/shell/browser/api/electron_api_app.cc
+++ b/shell/browser/api/electron_api_app.cc
@@ -1040,7 +1040,13 @@ std::string App::GetLocale() {
   return g_browser_process->GetApplicationLocale();
 }
 
-std::string App::GetSystemLocale() const {
+std::string App::GetSystemLocale(gin_helper::ErrorThrower thrower) const {
+  if (!Browser::Get()->is_ready()) {
+    thrower.ThrowError(
+        "app.getSystemLocale() can only be called "
+        "after app is ready");
+    return std::string();
+  }
   return static_cast<BrowserProcessImpl*>(g_browser_process)->GetSystemLocale();
 }
 
diff --git a/shell/browser/api/electron_api_app.h b/shell/browser/api/electron_api_app.h
index caf4459baced1..40f76b19148b1 100644
--- a/shell/browser/api/electron_api_app.h
+++ b/shell/browser/api/electron_api_app.h
@@ -191,7 +191,7 @@ class App : public ElectronBrowserClient::Delegate,
   void SetDesktopName(const std::string& desktop_name);
   std::string GetLocale();
   std::string GetLocaleCountryCode();
-  std::string GetSystemLocale() const;
+  std::string GetSystemLocale(gin_helper::ErrorThrower thrower) const;
   void OnSecondInstance(const base::CommandLine& cmd,
                         const base::FilePath& cwd,
                         const std::vector<const uint8_t> additional_data);
diff --git a/shell/browser/electron_browser_main_parts.cc b/shell/browser/electron_browser_main_parts.cc
index 41ee12687a1ca..748505ca85c5b 100644
--- a/shell/browser/electron_browser_main_parts.cc
+++ b/shell/browser/electron_browser_main_parts.cc
@@ -11,6 +11,7 @@
 #include "base/base_switches.h"
 #include "base/command_line.h"
 #include "base/feature_list.h"
+#include "base/i18n/rtl.h"
 #include "base/metrics/field_trial.h"
 #include "base/path_service.h"
 #include "base/run_loop.h"
@@ -285,6 +286,13 @@ int ElectronBrowserMainParts::PreCreateThreads() {
   if (!views::LayoutProvider::Get())
     layout_provider_ = std::make_unique<views::LayoutProvider>();
 
+    // Fetch the system locale for Electron.
+#if BUILDFLAG(IS_MAC)
+  fake_browser_process_->SetSystemLocale(GetCurrentSystemLocale());
+#else
+  fake_browser_process_->SetSystemLocale(base::i18n::GetConfiguredLocale());
+#endif
+
   auto* command_line = base::CommandLine::ForCurrentProcess();
   std::string locale = command_line->GetSwitchValueASCII(::switches::kLang);
 
@@ -320,10 +328,6 @@ int ElectronBrowserMainParts::PreCreateThreads() {
   }
 #endif
 
-  // Fetch the system locale for Electron.
-  fake_browser_process_->SetSystemLocale(
-      l10n_util::GetApplicationLocale("", false));
-
   // Initialize the app locale for Electron and Chromium.
   std::string app_locale = l10n_util::GetApplicationLocale(loaded_locale);
   ElectronBrowserClient::SetApplicationLocale(app_locale);
diff --git a/shell/browser/electron_browser_main_parts.h b/shell/browser/electron_browser_main_parts.h
index 3c45ed29bfbb7..3faabc559b951 100644
--- a/shell/browser/electron_browser_main_parts.h
+++ b/shell/browser/electron_browser_main_parts.h
@@ -130,6 +130,7 @@ class ElectronBrowserMainParts : public content::BrowserMainParts {
   void FreeAppDelegate();
   void RegisterURLHandler();
   void InitializeMainNib();
+  std::string GetSystemLocale();
 #endif
 
 #if BUILDFLAG(IS_MAC)
diff --git a/shell/browser/electron_browser_main_parts_mac.mm b/shell/browser/electron_browser_main_parts_mac.mm
index f280f66579f06..6dd69282feff7 100644
--- a/shell/browser/electron_browser_main_parts_mac.mm
+++ b/shell/browser/electron_browser_main_parts_mac.mm
@@ -4,6 +4,8 @@
 
 #include "shell/browser/electron_browser_main_parts.h"
 
+#include <string>
+
 #include "base/mac/bundle_locations.h"
 #include "base/mac/foundation_util.h"
 #include "base/path_service.h"
@@ -74,4 +76,23 @@
   [mainNib release];
 }
 
+std::string GetCurrentSystemLocale() {
+  NSString* systemLocaleIdentifier =
+      [[NSLocale currentLocale] localeIdentifier];
+
+  // Mac OS X uses "_" instead of "-", so swap to get a real locale value.
+  std::string locale_value = [[systemLocaleIdentifier
+      stringByReplacingOccurrencesOfString:@"_"
+                                withString:@"-"] UTF8String];
+
+  // On disk the "en-US" resources are just "en" (http://crbug.com/25578), so
+  // the reverse mapping is done here to continue to feed Chrome the same values
+  // in all cases on all platforms.  (l10n_util maps en to en-US if it gets
+  // passed this on the command line)
+  if (locale_value == "en")
+    locale_value = "en-US";
+
+  return locale_value;
+}
+
 }  // namespace electron