diff --git a/moto/identitystore/models.py b/moto/identitystore/models.py
--- a/moto/identitystore/models.py
+++ b/moto/identitystore/models.py
@@ -82,6 +82,12 @@ class IdentityStoreBackend(BaseBackend):
             "limit_default": 100,
             "unique_attribute": "MembershipId",
         },
+        "list_group_memberships_for_member": {
+            "input_token": "next_token",
+            "limit_key": "max_results",
+            "limit_default": 100,
+            "unique_attribute": "MembershipId",
+        },
         "list_groups": {
             "input_token": "next_token",
             "limit_key": "max_results",
@@ -264,6 +270,19 @@ def list_group_memberships(
             if m["GroupId"] == group_id
         ]
 
+    @paginate(pagination_model=PAGINATION_MODEL)  # type: ignore
+    def list_group_memberships_for_member(
+        self, identity_store_id: str, member_id: Dict[str, str]
+    ) -> List[Any]:
+        identity_store = self.__get_identity_store(identity_store_id)
+        user_id = member_id["UserId"]
+
+        return [
+            m
+            for m in identity_store.group_memberships.values()
+            if m["MemberId"]["UserId"] == user_id
+        ]
+
     @paginate(pagination_model=PAGINATION_MODEL)  # type: ignore
     def list_groups(
         self, identity_store_id: str, filters: List[Dict[str, str]]
diff --git a/moto/identitystore/responses.py b/moto/identitystore/responses.py
--- a/moto/identitystore/responses.py
+++ b/moto/identitystore/responses.py
@@ -137,6 +137,25 @@ def list_group_memberships(self) -> str:
             dict(GroupMemberships=group_memberships, NextToken=next_token)
         )
 
+    def list_group_memberships_for_member(self) -> str:
+        identity_store_id = self._get_param("IdentityStoreId")
+        member_id = self._get_param("MemberId")
+        max_results = self._get_param("MaxResults")
+        next_token = self._get_param("NextToken")
+        (
+            group_memberships,
+            next_token,
+        ) = self.identitystore_backend.list_group_memberships_for_member(
+            identity_store_id=identity_store_id,
+            member_id=member_id,
+            max_results=max_results,
+            next_token=next_token,
+        )
+
+        return json.dumps(
+            dict(GroupMemberships=group_memberships, NextToken=next_token)
+        )
+
     def list_groups(self) -> str:
         identity_store_id = self._get_param("IdentityStoreId")
         max_results = self._get_param("MaxResults")

diff --git a/tests/test_identitystore/test_identitystore.py b/tests/test_identitystore/test_identitystore.py
--- a/tests/test_identitystore/test_identitystore.py
+++ b/tests/test_identitystore/test_identitystore.py
@@ -560,6 +560,61 @@ def test_list_group_memberships():
             next_token = list_response["NextToken"]
 
 
+@mock_identitystore
+def test_list_group_memberships_for_member():
+    client = boto3.client("identitystore", region_name="us-east-2")
+    identity_store_id = get_identity_store_id()
+
+    start = 0
+    end = 5000
+    batch_size = 321
+    next_token = None
+    membership_ids = []
+
+    user_id = __create_and_verify_sparse_user(client, identity_store_id)["UserId"]
+    for i in range(end):
+        group_id = client.create_group(
+            IdentityStoreId=identity_store_id,
+            DisplayName=f"test_group_{i}",
+            Description="description",
+        )["GroupId"]
+        create_response = client.create_group_membership(
+            IdentityStoreId=identity_store_id,
+            GroupId=group_id,
+            MemberId={"UserId": user_id},
+        )
+        membership_ids.append((create_response["MembershipId"], user_id))
+
+    for iteration in range(start, end, batch_size):
+        last_iteration = end - iteration <= batch_size
+        expected_size = batch_size if not last_iteration else end - iteration
+        end_index = iteration + expected_size
+
+        if next_token is not None:
+            list_response = client.list_group_memberships_for_member(
+                IdentityStoreId=identity_store_id,
+                MemberId={"UserId": user_id},
+                MaxResults=batch_size,
+                NextToken=next_token,
+            )
+        else:
+            list_response = client.list_group_memberships_for_member(
+                IdentityStoreId=identity_store_id,
+                MemberId={"UserId": user_id},
+                MaxResults=batch_size,
+            )
+
+        assert len(list_response["GroupMemberships"]) == expected_size
+        __check_membership_list_values(
+            list_response["GroupMemberships"], membership_ids[iteration:end_index]
+        )
+        if last_iteration:
+            assert "NextToken" not in list_response
+        else:
+            assert "NextToken" in list_response
+            next_token = list_response["NextToken"]
+
+
 def __check_membership_list_values(members, expected):
     assert len(members) == len(expected)
     for i in range(len(expected)):

support list_group_memberships_for_member in identitystore
feature request for list_group_memberships_for_member

Ref: https://docs.getmoto.org/en/latest/docs/services/identitystore.html

tests/test_identitystore/test_identitystore.py::test_list_group_memberships_for_member
tests/test_identitystore/test_identitystore.py::test_create_username_missing_required_name_field[GivenName-familyname] tests/test_identitystore/test_identitystore.py::test_create_group_membership tests/test_identitystore/test_identitystore.py::test_list_users tests/test_identitystore/test_identitystore.py::test_describe_user_doesnt_exist tests/test_identitystore/test_identitystore.py::test_get_group_id tests/test_identitystore/test_identitystore.py::test_create_duplicate_username tests/test_identitystore/test_identitystore.py::test_create_describe_full_user tests/test_identitystore/test_identitystore.py::test_delete_group_membership tests/test_identitystore/test_identitystore.py::test_describe_group_doesnt_exist tests/test_identitystore/test_identitystore.py::test_delete_user tests/test_identitystore/test_identitystore.py::test_create_group_duplicate_name tests/test_identitystore/test_identitystore.py::test_create_username_missing_required_attributes tests/test_identitystore/test_identitystore.py::test_get_group_id_does_not_exist tests/test_identitystore/test_identitystore.py::test_create_describe_sparse_user tests/test_identitystore/test_identitystore.py::test_group_multiple_identity_stores tests/test_identitystore/test_identitystore.py::test_create_username_no_username tests/test_identitystore/test_identitystore.py::test_list_groups_filter tests/test_identitystore/test_identitystore.py::test_list_users_filter tests/test_identitystore/test_identitystore.py::test_create_username_missing_required_name_field[FamilyName-givenname] tests/test_identitystore/test_identitystore.py::test_list_group_memberships tests/test_identitystore/test_identitystore.py::test_delete_group tests/test_identitystore/test_identitystore.py::test_delete_user_doesnt_exist tests/test_identitystore/test_identitystore.py::test_create_describe_group tests/test_identitystore/test_identitystore.py::test_delete_group_doesnt_exist tests/test_identitystore/test_identitystore.py::test_list_groups tests/test_identitystore/test_identitystore.py::test_create_group