diff --git a/CHANGELOG.md b/CHANGELOG.md
index fc28054845..0154e2a0a8 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -16,6 +16,7 @@
   - Note: Expo Router span/breadcrumb attributes that may contain user identifiers (`route.href`, `route.params`, and concrete pathnames derived from string hrefs such as `/users/42`) are now gated behind `sendDefaultPii`. When `sendDefaultPii` is off (the default), prefetch spans for string hrefs use `route.name: 'unknown'` and omit `route.href`. Templated object hrefs (e.g. `{ pathname: '/users/[id]' }`) are unaffected.
 - Warn when Gradle resolves `sentry-android` to a version incompatible with the SDK ([#6238](https://github.com/getsentry/sentry-react-native/pull/6238))
 - Attach the active TurboModule method to native crash reports as `contexts.turbo_module` + `turbo_module.name` / `turbo_module.method` tags ([#6227](https://github.com/getsentry/sentry-react-native/pull/6227))
+- Warn during dev builds when multiple versions of Sentry JS SDK are detected ([#6269](https://github.com/getsentry/sentry-react-native/pull/6269))
 
 ### Fixes
 
diff --git a/packages/core/src/js/sdk.tsx b/packages/core/src/js/sdk.tsx
index 84cee9a088..9e4a877d84 100644
--- a/packages/core/src/js/sdk.tsx
+++ b/packages/core/src/js/sdk.tsx
@@ -31,6 +31,7 @@ import { DEFAULT_BUFFER_SIZE, makeNativeTransportFactory } from './transports/na
 import { getDefaultEnvironment, isExpoGo, isRunningInMetroDevServer, isWeb } from './utils/environment';
 import { getDefaultRelease } from './utils/release';
 import { safeFactory, safeTracesSampler } from './utils/safe';
+import { checkSentryJsSdkVersionMismatch } from './utils/sdkVersionCheck';
 import { RN_GLOBAL_OBJ } from './utils/worldwide';
 import { NATIVE } from './wrapper';
 
@@ -172,6 +173,7 @@ export function init(passedOptions: ReactNativeOptions): void {
     defaultIntegrations,
   });
   initAndBind(ReactNativeClient, options);
+  checkSentryJsSdkVersionMismatch();
 
   if (isExpoGo()) {
     debug.log('Offline caching, native errors features are not available in Expo Go.');
diff --git a/packages/core/src/js/utils/sdkVersionCheck.ts b/packages/core/src/js/utils/sdkVersionCheck.ts
new file mode 100644
index 0000000000..15098a4f82
--- /dev/null
+++ b/packages/core/src/js/utils/sdkVersionCheck.ts
@@ -0,0 +1,30 @@
+import { debug, getMainCarrier, SDK_VERSION as CORE_SDK_VERSION } from '@sentry/core';
+
+export function checkSentryJsSdkVersionMismatch(): void {
+  if (!__DEV__) {
+    return;
+  }
+
+  try {
+    const carrier = getMainCarrier();
+    const sentryCarrier = carrier.__SENTRY__;
+    if (!sentryCarrier) {
+      return;
+    }
+
+    const versions = Object.keys(sentryCarrier).filter(key => key !== CORE_SDK_VERSION && key !== 'version');
+    if (versions.length === 0) {
+      return;
+    }
+
+    debug.warn(
+      `Multiple versions of Sentry JavaScript SDKs were detected in your application. ` +
+        `Found versions: ${[CORE_SDK_VERSION, ...versions].join(', ')}. ` +
+        `This may cause unexpected behavior. ` +
+        `Ensure all Sentry packages use the same version. ` +
+        `See https://docs.sentry.io/platforms/react-native/troubleshooting/ for more details.`,
+    );
+  } catch (_e) {
+    // Ignore errors from version check
+  }
+}
diff --git a/packages/core/test/utils/sdkVersionCheck.test.ts b/packages/core/test/utils/sdkVersionCheck.test.ts
new file mode 100644
index 0000000000..954e078ce2
--- /dev/null
+++ b/packages/core/test/utils/sdkVersionCheck.test.ts
@@ -0,0 +1,93 @@
+const mockDebugWarn = jest.fn();
+const mockCarrier: Record<string, unknown> = {};
+
+jest.mock('@sentry/core', () => ({
+  debug: {
+    get warn() {
+      return mockDebugWarn;
+    },
+  },
+  getMainCarrier: () => mockCarrier,
+  SDK_VERSION: '10.0.0',
+}));
+
+import { checkSentryJsSdkVersionMismatch } from '../../src/js/utils/sdkVersionCheck';
+
+describe('checkSentryJsSdkVersionMismatch', () => {
+  beforeEach(() => {
+    jest.clearAllMocks();
+    delete mockCarrier.__SENTRY__;
+  });
+
+  it('does not warn when only one SDK version is present', () => {
+    mockCarrier.__SENTRY__ = { '10.0.0': {} };
+
+    checkSentryJsSdkVersionMismatch();
+
+    expect(mockDebugWarn).not.toHaveBeenCalled();
+  });
+
+  it('warns when multiple SDK versions are present', () => {
+    mockCarrier.__SENTRY__ = { '10.0.0': {}, '9.0.0': {} };
+
+    checkSentryJsSdkVersionMismatch();
+
+    expect(mockDebugWarn).toHaveBeenCalledTimes(1);
+    expect(mockDebugWarn).toHaveBeenCalledWith(expect.stringContaining('Multiple versions of Sentry JavaScript SDKs'));
+    expect(mockDebugWarn).toHaveBeenCalledWith(expect.stringContaining('9.0.0'));
+    expect(mockDebugWarn).toHaveBeenCalledWith(expect.stringContaining('10.0.0'));
+  });
+
+  it('warns when more than two SDK versions are present', () => {
+    mockCarrier.__SENTRY__ = { '10.0.0': {}, '9.0.0': {}, '8.0.0': {} };
+
+    checkSentryJsSdkVersionMismatch();
+
+    expect(mockDebugWarn).toHaveBeenCalledTimes(1);
+    expect(mockDebugWarn).toHaveBeenCalledWith(expect.stringContaining('9.0.0'));
+    expect(mockDebugWarn).toHaveBeenCalledWith(expect.stringContaining('8.0.0'));
+  });
+
+  it('does not warn when carrier has the version key set by @sentry/core', () => {
+    mockCarrier.__SENTRY__ = { '10.0.0': {}, version: '10.0.0' };
+
+    checkSentryJsSdkVersionMismatch();
+
+    expect(mockDebugWarn).not.toHaveBeenCalled();
+  });
+
+  it('does not warn when __SENTRY__ is not set', () => {
+    checkSentryJsSdkVersionMismatch();
+
+    expect(mockDebugWarn).not.toHaveBeenCalled();
+  });
+
+  it('does not warn in production builds', () => {
+    // @ts-expect-error -- __DEV__ is a RN global
+    globalThis.__DEV__ = false;
+    try {
+      mockCarrier.__SENTRY__ = { '10.0.0': {}, '9.0.0': {} };
+
+      checkSentryJsSdkVersionMismatch();
+
+      expect(mockDebugWarn).not.toHaveBeenCalled();
+    } finally {
+      // @ts-expect-error -- __DEV__ is a RN global
+      globalThis.__DEV__ = true;
+    }
+  });
+
+  it('does not throw on unexpected errors', () => {
+    Object.defineProperty(mockCarrier, '__SENTRY__', {
+      get() {
+        throw new Error('test error');
+      },
+      configurable: true,
+    });
+
+    expect(() => checkSentryJsSdkVersionMismatch()).not.toThrow();
+    expect(mockDebugWarn).not.toHaveBeenCalled();
+
+    delete mockCarrier.__SENTRY__;
+  });
+});