diff --git a/.github/.OwlBot.lock.yaml b/.github/.OwlBot.lock.yaml
index 55a7cb62..3f7634f2 100644
--- a/.github/.OwlBot.lock.yaml
+++ b/.github/.OwlBot.lock.yaml
@@ -13,6 +13,5 @@
 # limitations under the License.
 docker:
   image: gcr.io/cloud-devrel-public-resources/owlbot-python:latest
-  digest: sha256:631b4a35a4f9dd5e97740a97c4c117646eb85b35e103844dc49d152bd18694cd
-# created: 2025-02-05T14:40:56.685429494Z
-
+  digest: sha256:f016446d6e520e5fb552c45b110cba3f217bffdd3d06bdddd076e9e6d13266cf
+# created: 2025-02-21T19:32:52.01306189Z
diff --git a/.kokoro/build.sh b/.kokoro/build.sh
index 08171cbd..d41b45aa 100755
--- a/.kokoro/build.sh
+++ b/.kokoro/build.sh
@@ -15,11 +15,13 @@
 
 set -eo pipefail
 
+CURRENT_DIR=$(dirname "${BASH_SOURCE[0]}")
+
 if [[ -z "${PROJECT_ROOT:-}" ]]; then
-    PROJECT_ROOT="github/python-bigquery-pandas"
+  PROJECT_ROOT=$(realpath "${CURRENT_DIR}/..")
 fi
 
-cd "${PROJECT_ROOT}"
+pushd "${PROJECT_ROOT}"
 
 # Disable buffering, so that the logs stream through.
 export PYTHONUNBUFFERED=1
@@ -28,10 +30,16 @@ export PYTHONUNBUFFERED=1
 env | grep KOKORO
 
 # Setup service account credentials.
-export GOOGLE_APPLICATION_CREDENTIALS=${KOKORO_GFILE_DIR}/service-account.json
+if [[ -f "${KOKORO_GFILE_DIR}/service-account.json" ]]
+then
+  export GOOGLE_APPLICATION_CREDENTIALS=${KOKORO_GFILE_DIR}/service-account.json
+fi
 
 # Setup project id.
-export PROJECT_ID=$(cat "${KOKORO_GFILE_DIR}/project-id.json")
+if [[ -f "${KOKORO_GFILE_DIR}/project-id.json" ]]
+then
+  export PROJECT_ID=$(cat "${KOKORO_GFILE_DIR}/project-id.json")
+fi
 
 # If this is a continuous build, send the test log to the FlakyBot.
 # See https://github.com/googleapis/repo-automation-bots/tree/main/packages/flakybot.
@@ -46,7 +54,7 @@ fi
 # If NOX_SESSION is set, it only runs the specified session,
 # otherwise run all the sessions.
 if [[ -n "${NOX_SESSION:-}" ]]; then
-    python3 -m nox -s ${NOX_SESSION:-}
+  python3 -m nox -s ${NOX_SESSION:-}
 else
-    python3 -m nox
+  python3 -m nox
 fi
diff --git a/.readthedocs.yml b/.readthedocs.yml
index 7ae21e16..86e0f0fb 100644
--- a/.readthedocs.yml
+++ b/.readthedocs.yml
@@ -16,3 +16,9 @@ build:
 python:
   install:
   - requirements: docs/requirements-docs.txt
+
+# Explicit configuration path is required by ReadtheDocs starting Jan 20, 2025.
+# See: https://about.readthedocs.com/blog/2024/12/deprecate-config-files-without-sphinx-or-mkdocs-config/
+version: 2
+sphinx:
+  configuration: docs/conf.py
diff --git a/CHANGELOG.md b/CHANGELOG.md
index f628cddd..a860458b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,12 @@
 # Changelog
 
+## [0.28.0](https://github.com/googleapis/python-bigquery-pandas/compare/v0.27.0...v0.28.0) (2025-02-24)
+
+
+### Features
+
+* Add bigquery_client as a parameter for read_gbq and to_gbq ([#878](https://github.com/googleapis/python-bigquery-pandas/issues/878)) ([d42a562](https://github.com/googleapis/python-bigquery-pandas/commit/d42a56200fe2f356240c7956da4c201e872be4d5))
+
 ## [0.27.0](https://github.com/googleapis/python-bigquery-pandas/compare/v0.26.1...v0.27.0) (2025-02-05)
 
 
diff --git a/pandas_gbq/gbq.py b/pandas_gbq/gbq.py
index feffd858..bd3afb97 100644
--- a/pandas_gbq/gbq.py
+++ b/pandas_gbq/gbq.py
@@ -269,6 +269,7 @@ def __init__(
         client_secret=None,
         user_agent=None,
         rfc9110_delimiter=False,
+        bigquery_client=None,
     ):
         global context
         from google.api_core.exceptions import ClientError, GoogleAPIError
@@ -288,6 +289,14 @@ def __init__(
         self.client_secret = client_secret
         self.user_agent = user_agent
         self.rfc9110_delimiter = rfc9110_delimiter
+        self.use_bqstorage_api = use_bqstorage_api
+
+        if bigquery_client is not None:
+            # If a bq client is already provided, use it to populate auth fields.
+            self.project_id = bigquery_client.project
+            self.credentials = bigquery_client._credentials
+            self.client = bigquery_client
+            return
 
         default_project = None
 
@@ -325,8 +334,9 @@ def __init__(
         if context.project is None:
             context.project = self.project_id
 
-        self.client = self.get_client()
-        self.use_bqstorage_api = use_bqstorage_api
+        self.client = _get_client(
+            self.user_agent, self.rfc9110_delimiter, self.project_id, self.credentials
+        )
 
     def _start_timer(self):
         self.start = time.time()
@@ -702,6 +712,7 @@ def read_gbq(
     client_secret=None,
     *,
     col_order=None,
+    bigquery_client=None,
 ):
     r"""Read data from Google BigQuery to a pandas DataFrame.
 
@@ -849,6 +860,9 @@ def read_gbq(
         the user is attempting to connect to.
     col_order : list(str), optional
         Alias for columns, retained for backwards compatibility.
+    bigquery_client : google.cloud.bigquery.Client, optional
+        A Google Cloud BigQuery Python Client instance. If provided, it will be used for reading
+        data, while the project and credentials parameters will be ignored.
 
     Returns
     -------
@@ -900,6 +914,7 @@ def read_gbq(
         auth_redirect_uri=auth_redirect_uri,
         client_id=client_id,
         client_secret=client_secret,
+        bigquery_client=bigquery_client,
     )
 
     if _is_query(query_or_table):
@@ -971,6 +986,7 @@ def to_gbq(
     client_secret=None,
     user_agent=None,
     rfc9110_delimiter=False,
+    bigquery_client=None,
 ):
     """Write a DataFrame to a Google BigQuery table.
 
@@ -1087,6 +1103,9 @@ def to_gbq(
     rfc9110_delimiter : bool
         Sets user agent delimiter to a hyphen or a slash.
         Default is False, meaning a hyphen will be used.
+    bigquery_client : google.cloud.bigquery.Client, optional
+        A Google Cloud BigQuery Python Client instance. If provided, it will be used for reading
+        data, while the project, user_agent, and credentials parameters will be ignored.
 
         .. versionadded:: 0.23.3
     """
@@ -1157,6 +1176,7 @@ def to_gbq(
         client_secret=client_secret,
         user_agent=user_agent,
         rfc9110_delimiter=rfc9110_delimiter,
+        bigquery_client=bigquery_client,
     )
     bqclient = connector.client
 
@@ -1492,3 +1512,22 @@ def create_user_agent(
         user_agent = f"{user_agent} {identity}"
 
     return user_agent
+
+
+def _get_client(user_agent, rfc9110_delimiter, project_id, credentials):
+    import google.api_core.client_info
+
+    bigquery = FEATURES.bigquery_try_import()
+
+    user_agent = create_user_agent(
+        user_agent=user_agent, rfc9110_delimiter=rfc9110_delimiter
+    )
+
+    client_info = google.api_core.client_info.ClientInfo(
+        user_agent=user_agent,
+    )
+    return bigquery.Client(
+        project=project_id,
+        credentials=credentials,
+        client_info=client_info,
+    )
diff --git a/pandas_gbq/version.py b/pandas_gbq/version.py
index e9325b39..a6070398 100644
--- a/pandas_gbq/version.py
+++ b/pandas_gbq/version.py
@@ -2,4 +2,4 @@
 # Use of this source code is governed by a BSD-style
 # license that can be found in the LICENSE file.
 
-__version__ = "0.27.0"
+__version__ = "0.28.0"
diff --git a/tests/system/conftest.py b/tests/system/conftest.py
index 8c45167f..cb8aadb9 100644
--- a/tests/system/conftest.py
+++ b/tests/system/conftest.py
@@ -54,6 +54,13 @@ def to_gbq(credentials, project_id):
     )
 
 
+@pytest.fixture
+def to_gbq_with_bq_client(bigquery_client):
+    import pandas_gbq
+
+    return functools.partial(pandas_gbq.to_gbq, bigquery_client=bigquery_client)
+
+
 @pytest.fixture
 def read_gbq(credentials, project_id):
     import pandas_gbq
@@ -63,6 +70,13 @@ def read_gbq(credentials, project_id):
     )
 
 
+@pytest.fixture
+def read_gbq_with_bq_client(bigquery_client):
+    import pandas_gbq
+
+    return functools.partial(pandas_gbq.read_gbq, bigquery_client=bigquery_client)
+
+
 @pytest.fixture()
 def random_dataset_id(bigquery_client: bigquery.Client, project_id: str):
     dataset_id = prefixer.create_prefix()
diff --git a/tests/system/test_gbq.py b/tests/system/test_gbq.py
index b62f3590..1457ec30 100644
--- a/tests/system/test_gbq.py
+++ b/tests/system/test_gbq.py
@@ -1398,3 +1398,13 @@ def test_to_gbq_does_not_override_mode(gbq_table, gbq_connector):
     )
 
     assert verify_schema(gbq_connector, gbq_table.dataset_id, table_id, table_schema)
+
+
+def test_gbqconnector_init_with_bq_client(bigquery_client):
+    gbq_connector = gbq.GbqConnector(
+        project_id="project_id", credentials=None, bigquery_client=bigquery_client
+    )
+
+    assert gbq_connector.project_id == bigquery_client.project
+    assert gbq_connector.credentials is bigquery_client._credentials
+    assert gbq_connector.client is bigquery_client
diff --git a/tests/system/test_read_gbq.py b/tests/system/test_read_gbq.py
index 4ae96a36..72cb6b66 100644
--- a/tests/system/test_read_gbq.py
+++ b/tests/system/test_read_gbq.py
@@ -659,3 +659,14 @@ def test_dml_query(read_gbq, writable_table: str):
     """
     result = read_gbq(query)
     assert result is not None
+
+
+def test_read_gbq_with_bq_client(read_gbq_with_bq_client):
+    query = "SELECT * FROM UNNEST([1, 2, 3]) AS numbers"
+
+    actual_result = read_gbq_with_bq_client(query)
+
+    expected_result = pandas.DataFrame(
+        {"numbers": pandas.Series([1, 2, 3], dtype="Int64")}
+    )
+    pandas.testing.assert_frame_equal(actual_result, expected_result)
diff --git a/tests/system/test_to_gbq.py b/tests/system/test_to_gbq.py
index 139f072b..ad7c58ec 100644
--- a/tests/system/test_to_gbq.py
+++ b/tests/system/test_to_gbq.py
@@ -615,3 +615,17 @@ def test_dataframe_round_trip_with_table_schema(
     pandas.testing.assert_frame_equal(
         expected_df.set_index("row_num").sort_index(), round_trip
     )
+
+
+def test_dataframe_round_trip_with_bq_client(
+    to_gbq_with_bq_client, read_gbq_with_bq_client, random_dataset_id
+):
+    table_id = (
+        f"{random_dataset_id}.round_trip_w_bq_client_{random.randrange(1_000_000)}"
+    )
+    df = pandas.DataFrame({"numbers": pandas.Series([1, 2, 3], dtype="Int64")})
+
+    to_gbq_with_bq_client(df, table_id)
+    result = read_gbq_with_bq_client(table_id)
+
+    pandas.testing.assert_frame_equal(result, df)