diff --git a/google/auth/transport/requests.py b/google/auth/transport/requests.py
index ce78e63..1c709d4 100644
--- a/google/auth/transport/requests.py
+++ b/google/auth/transport/requests.py
@@ -42,6 +42,8 @@
 
 _LOGGER = logging.getLogger(__name__)
 
+_DEFAULT_TIMEOUT = 120  # in seconds
+
 
 class _Response(transport.Response):
     """Requests transport response adapter.
@@ -141,7 +143,13 @@
         self.session = session
 
     def __call__(
-        self, url, method="GET", body=None, headers=None, timeout=120, **kwargs
+        self,
+        url,
+        method="GET",
+        body=None,
+        headers=None,
+        timeout=_DEFAULT_TIMEOUT,
+        **kwargs
     ):
         """Make an HTTP request using requests.
 
@@ -246,7 +254,7 @@
         data=None,
         headers=None,
         max_allowed_time=None,
-        timeout=None,
+        timeout=_DEFAULT_TIMEOUT,
         **kwargs
     ):
         """Implementation of Requests' request.
diff --git a/tests/transport/test_requests.py b/tests/transport/test_requests.py
index 8f73d4b..f0321c8 100644
--- a/tests/transport/test_requests.py
+++ b/tests/transport/test_requests.py
@@ -177,6 +177,21 @@
 
         assert authed_session._auth_request == auth_request
 
+    def test_request_default_timeout(self):
+        credentials = mock.Mock(wraps=CredentialsStub())
+        response = make_response()
+        adapter = AdapterStub([response])
+
+        authed_session = google.auth.transport.requests.AuthorizedSession(credentials)
+        authed_session.mount(self.TEST_URL, adapter)
+
+        patcher = mock.patch("google.auth.transport.requests.requests.Session.request")
+        with patcher as patched_request:
+            authed_session.request("GET", self.TEST_URL)
+
+        expected_timeout = google.auth.transport.requests._DEFAULT_TIMEOUT
+        assert patched_request.call_args.kwargs.get("timeout") == expected_timeout
+
     def test_request_no_refresh(self):
         credentials = mock.Mock(wraps=CredentialsStub())
         response = make_response()