diff --git a/changelog.d/12195.feature b/changelog.d/12195.feature
new file mode 100644
index 000000000000..e8bcb950a1c6
--- /dev/null
+++ b/changelog.d/12195.feature
@@ -0,0 +1 @@
+Allow modules to store already existing 3PID associations.
diff --git a/synapse/module_api/__init__.py b/synapse/module_api/__init__.py
index c42eeedd87ae..bcd4f05664e8 100644
--- a/synapse/module_api/__init__.py
+++ b/synapse/module_api/__init__.py
@@ -659,7 +659,8 @@ def register_device(
     def record_user_external_id(
         self, auth_provider_id: str, remote_user_id: str, registered_user_id: str
     ) -> defer.Deferred:
-        """Record a mapping from an external user id to a mxid
+        """Record a mapping between an external user id from a single sign-on provider
+        and a mxid.
 
         Added in Synapse v1.9.0.
 
@@ -1274,6 +1275,30 @@ async def check_username(self, username: str) -> None:
         """
         await self._registration_handler.check_username(username)
 
+    async def store_remote_3pid_association(
+        self, user_id: str, medium: str, address: str, id_server: str
+    ) -> None:
+        """Stores an existing association between a user ID and a third-party identifier.
+
+        The association must already exist on the remote identity server.
+
+        Added in Synapse v1.56.0.
+
+        Args:
+            user_id: The user ID that's been associated with the 3PID.
+            medium: The medium of the 3PID (current supported values are "msisdn" and
+                "email").
+            address: The address of the 3PID.
+            id_server: The identity server the 3PID association has been registered on.
+                This should only be the domain (or IP address, optionally with the port
+                number) for the identity server. This will be used to reach out to the
+                identity server using HTTPS (unless specified otherwise by Synapse's
+                configuration) when attempting to unbind the third-party identifier.
+
+
+        """
+        await self._store.add_user_bound_threepid(user_id, medium, address, id_server)
+
 
 class PublicRoomListManager:
     """Contains methods for adding to, removing from and querying whether a room