diff --git a/CHANGELOG.md b/CHANGELOG.md
index 1f0e1b955..c399a87a9 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,10 @@
 
 ## Unreleased
 
+## Fixed
+
+- Google Big Query: get project_id from connector config whatever auth mode (JWT/GoogleCreds).
+
 ### [4.9.1] 2023-09-22
 
 ## Fixed
diff --git a/tests/google_big_query/test_google_big_query.py b/tests/google_big_query/test_google_big_query.py
index 64851b99d..a0c72fe43 100644
--- a/tests/google_big_query/test_google_big_query.py
+++ b/tests/google_big_query/test_google_big_query.py
@@ -771,6 +771,37 @@ def mock_available_schs():
         == 'THE_JWT_project_id'
     )
 
+    # Now let say the JWT is not set or bad, or the project_id is also bad or
+    # not set, we need to fallback on project_id provided by the GoogleCreds
+    assert (
+        GoogleBigQueryDataSource(query=',', name='MyGBQ-WITH-JWT', domain='foo').get_form(
+            GoogleBigQueryConnector(
+                name='MyGBQ',
+                credentials=GoogleCredentials(
+                    type='my_type',
+                    project_id='THE_GOOGLE_CREDS_project_id',
+                    private_key_id='my_private_key_id',
+                    private_key='my_private_key',
+                    client_email='my_client_email@email.com',
+                    client_id='my_client_id',
+                    auth_uri='https://accounts.google.com/o/oauth2/auth',
+                    token_uri='https://oauth2.googleapis.com/token',
+                    auth_provider_x509_cert_url='https://www.googleapis.com/oauth2/v1/certs',
+                    client_x509_cert_url='https://www.googleapis.com/robot/v1/metadata/x509/pika.com',
+                ),
+                jwt_credentials=JWTCredentials(
+                    project_id='THE_JWT_project_id',
+                    jwt_token='',  # the jwt is empty
+                ),
+                scopes=[
+                    'https://www.googleapis.com/auth/bigquery',
+                ],
+            ),
+            {},
+        )['properties']['database']['default']
+        == 'THE_GOOGLE_CREDS_project_id'  # because the jwt_token value is not good or missing
+    )
+
 
 @pytest.mark.parametrize(
     'input_query, expected_output',
@@ -852,3 +883,34 @@ def test_optional_fields_validator_for_google_creds_or_jwt():
     }
     # no error raised
     _ = GoogleBigQueryConnector(name='something', jwt_credentials=valid_credentials)
+
+
+def test_get_project_id(_fixture_credentials: GoogleCredentials) -> None:
+    connector = GoogleBigQueryConnector(
+        name='MyGBQ',
+        credentials=_fixture_credentials,
+        jwt_credentials=JWTCredentials(jwt_token='token', project_id='123'),
+        scopes=[
+            'https://www.googleapis.com/auth/bigquery',
+            'https://www.googleapis.com/auth/drive',
+        ],
+    )
+
+    # test get project id with jwt credentials
+    assert connector._get_project_id() == '123'
+
+    # test get project id with credentials
+    connector.jwt_credentials = None
+    connector.credentials = _fixture_credentials
+    connector.credentials.project_id = '456'
+    assert connector._get_project_id() == '456'
+
+    # On ProjectId missing...
+    connector = GoogleBigQueryConnector(
+        name='MyGBQ',
+        credentials=None,
+        jwt_credentials=JWTCredentials(jwt_token='', project_id=''),
+        scopes=[],
+    )
+    with pytest.raises(GoogleClientCreationError):
+        connector._get_project_id()
diff --git a/toucan_connectors/google_big_query/google_big_query_connector.py b/toucan_connectors/google_big_query/google_big_query_connector.py
index 0a37a2519..4025b73cc 100644
--- a/toucan_connectors/google_big_query/google_big_query_connector.py
+++ b/toucan_connectors/google_big_query/google_big_query_connector.py
@@ -102,13 +102,7 @@ def get_form(cls, connector: 'GoogleBigQueryConnector', current_config: dict[str
             __base__=cls,
         ).schema()
 
-        project_id = ''
-        if connector.jwt_credentials:
-            project_id = connector.jwt_credentials.project_id
-        elif connector.credentials:
-            project_id = connector.credentials.project_id
-
-        schema['properties']['database']['default'] = project_id
+        schema['properties']['database']['default'] = connector._get_project_id()
 
         return schema
 
@@ -320,7 +314,7 @@ def _bigquery_client(self) -> bigquery.Client:
                 # We try to instantiate the bigquery.Client with the given jwt-token
                 _session = CustomRequestSession(self.jwt_credentials.jwt_token)
                 client = GoogleBigQueryConnector._http_connect(
-                    http_session=_session, project_id=self.jwt_credentials.project_id
+                    http_session=_session, project_id=self._get_project_id()
                 )
                 _LOGGER.info('bigqueryClient created with the JWT provided !')
 
@@ -332,6 +326,22 @@ def _bigquery_client(self) -> bigquery.Client:
         # or we fallback on default google-credentials
         return self._bigquery_client_with_google_creds()
 
+    def _get_project_id(self) -> str:
+        """We need an util in other to check either jwt_creds are well set or
+        not for the configuration validation, because self.jwt_credentials can
+        be not None but its value are either empty or None..."""
+        if (
+            self.jwt_credentials
+            and self.jwt_credentials.jwt_token
+            and self.jwt_credentials.project_id
+        ):
+            return self.jwt_credentials.project_id
+        elif self.credentials and self.credentials.project_id:
+            return self.credentials.project_id
+        else:
+            # project-id is missing and it's mandatory
+            raise GoogleClientCreationError
+
     def _get_bigquery_client(self) -> bigquery.Client:
         with suppress(Exception):
             if bigquery_client := self._bigquery_client: