diff --git a/.changes/next-release/bugfix-Config-98372.json b/.changes/next-release/bugfix-Config-98372.json
new file mode 100644
index 0000000000..d1f5a51c05
--- /dev/null
+++ b/.changes/next-release/bugfix-Config-98372.json
@@ -0,0 +1,5 @@
+{
+  "type": "bugfix",
+  "category": "Config",
+  "description": "Fixed sigv4a_signing_region_set resolution when set in environment or config file."
+}
diff --git a/botocore/args.py b/botocore/args.py
index 741ca77886..aeb9ff4198 100644
--- a/botocore/args.py
+++ b/botocore/args.py
@@ -276,6 +276,7 @@ def compute_client_args(
         self._compute_connect_timeout(config_kwargs)
         self._compute_user_agent_appid_config(config_kwargs)
         self._compute_request_compression_config(config_kwargs)
+        self._compute_sigv4a_signing_region_set_config(config_kwargs)
         s3_config = self.compute_s3_config(client_config)
 
         is_s3_service = self._is_s3_service(service_name)
@@ -771,3 +772,13 @@ def _compute_user_agent_appid_config(self, config_kwargs):
                 f'maximum length of {USERAGENT_APPID_MAXLEN} characters.'
             )
         config_kwargs['user_agent_appid'] = user_agent_appid
+
+    def _compute_sigv4a_signing_region_set_config(self, config_kwargs):
+        sigv4a_signing_region_set = config_kwargs.get(
+            'sigv4a_signing_region_set'
+        )
+        if sigv4a_signing_region_set is None:
+            sigv4a_signing_region_set = self._config_store.get_config_variable(
+                'sigv4a_signing_region_set'
+            )
+        config_kwargs['sigv4a_signing_region_set'] = sigv4a_signing_region_set
diff --git a/tests/functional/test_auth_config.py b/tests/functional/test_auth_config.py
index 7fe096d338..489ade6ad5 100644
--- a/tests/functional/test_auth_config.py
+++ b/tests/functional/test_auth_config.py
@@ -12,7 +12,8 @@
 # language governing permissions and limitations under the License.
 import pytest
 
-from botocore.session import get_session
+from botocore.config import Config
+from tests import create_session, mock
 
 # In the future, a service may have a list of credentials requirements where one
 # signature may fail and others may succeed. e.g. a service may want to use bearer
@@ -31,7 +32,7 @@
 
 
 def _all_test_cases():
-    session = get_session()
+    session = create_session()
     loader = session.get_component('data_loader')
 
     services = loader.list_available_services('service-2')
@@ -74,4 +75,49 @@ def assert_all_requirements_match(auth_config, message):
     auth_requirements = set(
         AUTH_TYPE_REQUIREMENTS[auth_type] for auth_type in auth_config
     )
-    assert len(auth_requirements) == 1
+    assert len(auth_requirements) == 1, message
+
+
+def get_config_file_path(base_path, value):
+    if value is None:
+        return "file-does-not-exist"
+
+    tmp_config_file_path = base_path / "config"
+    tmp_config_file_path.write_text(
+        f"[default]\nsigv4a_signing_region_set={value}\n"
+    )
+    return tmp_config_file_path
+
+
+def get_environ_mock(
+    request,
+    env_var_value=None,
+    config_file_value=None,
+):
+    base_path = request.getfixturevalue("tmp_path")
+    config_file_path = get_config_file_path(base_path, config_file_value)
+    return {
+        "AWS_CONFIG_FILE": str(config_file_path),
+        "AWS_SIGV4A_SIGNING_REGION_SET": env_var_value,
+    }
+
+
+@pytest.mark.parametrize(
+    "client_config, env_var_val, config_file_val, expected",
+    [
+        (Config(sigv4a_signing_region_set="foo"), "bar", "baz", "foo"),
+        (Config(sigv4a_signing_region_set="foo"), None, None, "foo"),
+        (None, "bar", "baz", "bar"),
+        (None, None, "baz", "baz"),
+        (Config(sigv4a_signing_region_set="foo"), None, "baz", "foo"),
+        (None, None, None, None),
+    ],
+)
+def test_sigv4a_signing_region_set_config_from_environment(
+    client_config, env_var_val, config_file_val, expected, request
+):
+    environ_mock = get_environ_mock(request, env_var_val, config_file_val)
+    with mock.patch('os.environ', environ_mock):
+        session = create_session()
+        s3 = session.create_client('s3', config=client_config)
+        assert s3.meta.config.sigv4a_signing_region_set == expected