diff --git a/synapse/events/third_party_rules.py b/synapse/events/third_party_rules.py
index 72ab696898..0577085be8 100644
--- a/synapse/events/third_party_rules.py
+++ b/synapse/events/third_party_rules.py
@@ -45,6 +45,7 @@ CHECK_CAN_DEACTIVATE_USER_CALLBACK = Callable[[str, bool], Awaitable[bool]]
 ON_PROFILE_UPDATE_CALLBACK = Callable[[str, ProfileInfo, bool, bool], Awaitable]
 ON_USER_DEACTIVATION_STATUS_CHANGED_CALLBACK = Callable[[str, bool, bool], Awaitable]
 ON_THREEPID_BIND_CALLBACK = Callable[[str, str, str], Awaitable]
+ON_UPDATE_IDENTITY_SERVER_BINDING_CALLBACK = Callable[[str, str, str, Optional[str]], Awaitable[bool]]
 
 
 def load_legacy_third_party_event_rules(hs: "HomeServer") -> None:
@@ -174,6 +175,7 @@ class ThirdPartyEventRules:
             ON_USER_DEACTIVATION_STATUS_CHANGED_CALLBACK
         ] = []
         self._on_threepid_bind_callbacks: List[ON_THREEPID_BIND_CALLBACK] = []
+        self._on_update_identity_server_binding: List[ON_UPDATE_IDENTITY_SERVER_BINDING_CALLBACK] = []
 
     def register_third_party_rules_callbacks(
         self,
@@ -193,6 +195,7 @@ class ThirdPartyEventRules:
             ON_USER_DEACTIVATION_STATUS_CHANGED_CALLBACK
         ] = None,
         on_threepid_bind: Optional[ON_THREEPID_BIND_CALLBACK] = None,
+        on_update_identity_server_binding: Optional[ON_UPDATE_IDENTITY_SERVER_BINDING_CALLBACK] = None,
     ) -> None:
         """Register callbacks from modules for each hook."""
         if check_event_allowed is not None:
@@ -230,6 +233,9 @@ class ThirdPartyEventRules:
         if on_threepid_bind is not None:
             self._on_threepid_bind_callbacks.append(on_threepid_bind)
 
+        if on_update_identity_server_binding is not None:
+            self._on_update_identity_server_binding.append(on_update_identity_server_binding)
+
     async def check_event_allowed(
         self, event: EventBase, context: EventContext
     ) -> Tuple[bool, Optional[dict]]:
@@ -523,3 +529,24 @@ class ThirdPartyEventRules:
                 logger.exception(
                     "Failed to run module API callback %s: %s", callback, e
                 )
+    async def on_update_identity_server_binding(self, user_id: str, medium: str, address: str, id_server: Optional[str]) -> bool:
+        """Called before a binding between a third-party ID and a Matrix ID is made
+        against an identity server.
+
+        Note that this callback is not called if a user only requests for an association
+        to be made between a third-party ID and their Matrix on their local homeserver.
+        It is only called if an identity server is to receive the binding as well.
+
+        Args:
+            user_id: the ID of the user to include in the association.
+            medium: the medium of the third-party ID (email, msisdn).
+            address: the address of the third-party ID (i.e. an email address).
+            id_server:
+        """
+        for callback in self._on_threepid_bind_callbacks:
+            try:
+                await callback(user_id, medium, address)
+            except Exception as e:
+                logger.exception(
+                    "Failed to run module API callback %s: %s", callback, e
+                )
diff --git a/synapse/module_api/__init__.py b/synapse/module_api/__init__.py
index d22dd19d38..ec7495bf40 100644
--- a/synapse/module_api/__init__.py
+++ b/synapse/module_api/__init__.py
@@ -68,6 +68,7 @@ from synapse.events.third_party_rules import (
     ON_NEW_EVENT_CALLBACK,
     ON_PROFILE_UPDATE_CALLBACK,
     ON_THREEPID_BIND_CALLBACK,
+    ON_UPDATE_IDENTITY_SERVER_BINDING_CALLBACK,
     ON_USER_DEACTIVATION_STATUS_CHANGED_CALLBACK,
 )
 from synapse.handlers.account_data import ON_ACCOUNT_DATA_UPDATED_CALLBACK
@@ -357,6 +358,7 @@ class ModuleApi:
             ON_USER_DEACTIVATION_STATUS_CHANGED_CALLBACK
         ] = None,
         on_threepid_bind: Optional[ON_THREEPID_BIND_CALLBACK] = None,
+        on_update_identity_server_binding: Optional[ON_UPDATE_IDENTITY_SERVER_BINDING_CALLBACK] = None,
     ) -> None:
         """Registers callbacks for third party event rules capabilities.
 
@@ -373,6 +375,7 @@ class ModuleApi:
             on_profile_update=on_profile_update,
             on_user_deactivation_status_changed=on_user_deactivation_status_changed,
             on_threepid_bind=on_threepid_bind,
+            on_update_identity_server_binding=on_update_identity_server_binding,
         )
 
     def register_presence_router_callbacks(