diff --git a/src/browser.ts b/src/browser.ts
index b15b5efa4..63221a3f7 100644
--- a/src/browser.ts
+++ b/src/browser.ts
@@ -14,8 +14,14 @@ import type {
   ChromeReleaseChannel,
   LaunchOptions,
   Target,
+  BrowsersChromeReleaseChannel,
+} from './third_party/index.js';
+import {
+  puppeteer,
+  resolveDefaultUserDataDir,
+  detectBrowserPlatform,
+  BrowserEnum,
 } from './third_party/index.js';
-import {puppeteer} from './third_party/index.js';
 
 let browser: Browser | undefined;
 
@@ -49,6 +55,7 @@ export async function ensureBrowserConnected(options: {
   wsHeaders?: Record<string, string>;
   devtools: boolean;
   channel?: Channel;
+  userDataDir?: string;
 }) {
   const {channel} = options;
   if (browser?.connected) {
@@ -68,15 +75,57 @@ export async function ensureBrowserConnected(options: {
     }
   } else if (options.browserURL) {
     connectOptions.browserURL = options.browserURL;
-  } else if (channel) {
-    const puppeteerChannel =
-      channel !== 'stable'
-        ? (`chrome-${channel}` as ChromeReleaseChannel)
-        : 'chrome';
-    connectOptions.channel = puppeteerChannel;
+  } else if (channel || options.userDataDir) {
+    let userDataDir = options.userDataDir;
+    if (!userDataDir) {
+      if (!channel) {
+        throw new Error('Channel must be provided if userDataDir is missing');
+      }
+      const platform = detectBrowserPlatform();
+      if (!platform) {
+        throw new Error('Could not detect required browser platform');
+      }
+      userDataDir = resolveDefaultUserDataDir(
+        BrowserEnum.CHROME,
+        platform,
+        (channel === 'stable'
+          ? 'chrome'
+          : `chrome-${channel}`) as BrowsersChromeReleaseChannel,
+      );
+    }
+
+    // TODO: re-expose this logic via Puppeteer.
+    const portPath = path.join(userDataDir, 'DevToolsActivePort');
+    try {
+      const fileContent = await fs.promises.readFile(portPath, 'utf8');
+      const [rawPort, rawPath] = fileContent
+        .split('\n')
+        .map(line => {
+          return line.trim();
+        })
+        .filter(line => {
+          return !!line;
+        });
+      if (!rawPort || !rawPath) {
+        throw new Error(`Invalid DevToolsActivePort '${fileContent}' found`);
+      }
+      const port = parseInt(rawPort, 10);
+      if (isNaN(port) || port <= 0 || port > 65535) {
+        throw new Error(`Invalid port '${rawPort}' found`);
+      }
+      const browserWSEndpoint = `ws://127.0.0.1:${port}${rawPath}`;
+      connectOptions.browserWSEndpoint = browserWSEndpoint;
+    } catch (error) {
+      throw new Error(
+        `Could not connect to Chrome in ${userDataDir}. Check if Chrome is running and remote debugging is enabled.`,
+        {
+          cause: error,
+        },
+      );
+    }
   } else {
     throw new Error(
-      'Either browserURL, wsEndpoint or channel must be provided',
+      'Either browserURL, wsEndpoint, channel or userDataDir must be provided',
     );
   }
 
diff --git a/src/cli.ts b/src/cli.ts
index 9da407510..3e25f8d6c 100644
--- a/src/cli.ts
+++ b/src/cli.ts
@@ -12,7 +12,7 @@ export const cliOptions = {
     type: 'boolean',
     description:
       'If specified, automatically connects to a browser (Chrome 145+) running in the user data directory identified by the channel param.',
-    conflicts: ['isolated', 'executablePath', 'userDataDir'],
+    conflicts: ['isolated', 'executablePath'],
     default: false,
     coerce: (value: boolean | undefined) => {
       if (!value) {
diff --git a/src/main.ts b/src/main.ts
index e785e9c74..ca02a6472 100644
--- a/src/main.ts
+++ b/src/main.ts
@@ -61,6 +61,7 @@ async function getContext(): Promise<McpContext> {
           wsHeaders: args.wsHeaders,
           // Important: only pass channel, if autoConnect is true.
           channel: args.autoConnect ? (args.channel as Channel) : undefined,
+          userDataDir: args.userDataDir,
           devtools,
         })
       : await ensureBrowserLaunched({
diff --git a/src/third_party/index.ts b/src/third_party/index.ts
index 83194e38a..fc589fcc0 100644
--- a/src/third_party/index.ts
+++ b/src/third_party/index.ts
@@ -29,3 +29,9 @@ export {
 export {default as puppeteer} from 'puppeteer-core';
 export type * from 'puppeteer-core';
 export type {CdpPage} from 'puppeteer-core/internal/cdp/Page.js';
+export {
+  resolveDefaultUserDataDir,
+  detectBrowserPlatform,
+  Browser as BrowserEnum,
+  type ChromeReleaseChannel as BrowsersChromeReleaseChannel,
+} from '@puppeteer/browsers';
diff --git a/tests/browser.test.ts b/tests/browser.test.ts
index 3c8e31ca8..1519a62fd 100644
--- a/tests/browser.test.ts
+++ b/tests/browser.test.ts
@@ -11,7 +11,7 @@ import {describe, it} from 'node:test';
 
 import {executablePath} from 'puppeteer';
 
-import {launch} from '../src/browser.js';
+import {ensureBrowserConnected, launch} from '../src/browser.js';
 
 describe('browser', () => {
   it('cannot launch multiple times with the same profile', async () => {
@@ -73,4 +73,27 @@ describe('browser', () => {
       await browser.close();
     }
   });
+  it('connects to an existing browser with userDataDir', async () => {
+    const tmpDir = os.tmpdir();
+    const folderPath = path.join(tmpDir, `temp-folder-${crypto.randomUUID()}`);
+    const browser = await launch({
+      headless: true,
+      isolated: false,
+      userDataDir: folderPath,
+      executablePath: executablePath(),
+      devtools: false,
+      args: ['--remote-debugging-port=0'],
+    });
+    try {
+      const connectedBrowser = await ensureBrowserConnected({
+        userDataDir: folderPath,
+        devtools: false,
+      });
+      assert.ok(connectedBrowser);
+      assert.ok(connectedBrowser.isConnected());
+      connectedBrowser.disconnect();
+    } finally {
+      await browser.close();
+    }
+  });
 });