diff --git a/changelog.d/18040.feature b/changelog.d/18040.feature
new file mode 100644
index 00000000000..76c41cd08f0
--- /dev/null
+++ b/changelog.d/18040.feature
@@ -0,0 +1 @@
+Add a query param `participant` to `/members` admin api to filter for room participants.
\ No newline at end of file
diff --git a/docs/admin_api/rooms.md b/docs/admin_api/rooms.md
index 8e3a367e90a..442ad3b15ec 100644
--- a/docs/admin_api/rooms.md
+++ b/docs/admin_api/rooms.md
@@ -358,6 +358,13 @@ The API is:
 GET /_synapse/admin/v1/rooms/<room_id>/members
 ```
 
+**Parameters**
+
+The following query parameters are available:
+
+* `participant` - Optional. If provided and set to true, only returns currently joined members who have
+  also posted to the room. Defaults to false. 
+
 A response body like the following is returned:
 
 ```json
diff --git a/synapse/rest/admin/rooms.py b/synapse/rest/admin/rooms.py
index 01f9de9ffa5..794c8118720 100644
--- a/synapse/rest/admin/rooms.py
+++ b/synapse/rest/admin/rooms.py
@@ -434,7 +434,12 @@ async def on_GET(
         if not room:
             raise NotFoundError("Room not found")
 
-        members = await self.store.get_users_in_room(room_id)
+        participant = parse_boolean(request, "participant", False)
+
+        if participant:
+            members = await self.store.get_participants_in_room(room_id)
+        else:
+            members = await self.store.get_users_in_room(room_id)
         ret = {"members": members, "total": len(members)}
 
         return HTTPStatus.OK, ret
diff --git a/synapse/storage/databases/main/roommember.py b/synapse/storage/databases/main/roommember.py
index 50ed6a28bf0..d386dd8499a 100644
--- a/synapse/storage/databases/main/roommember.py
+++ b/synapse/storage/databases/main/roommember.py
@@ -1606,6 +1606,34 @@ def _get_rooms_for_user_by_join_date_txn(
             from_ts,
         )
 
+    async def get_participants_in_room(self, room_id: str) -> Sequence[str]:
+        """
+        Return a list of all currently joined room members who have posted
+        in the given room.
+
+        Args:
+            room_id: room ID of the room to search in
+        """
+
+        def _get_participants_in_room_txn(
+            txn: LoggingTransaction, room_id: str
+        ) -> List[str]:
+            sql = """
+                SELECT DISTINCT c.state_key
+                FROM current_state_events AS c
+                INNER JOIN events AS e USING(room_id)
+                WHERE room_id = ?
+                    AND c.membership = 'join'
+                    AND e.type = 'm.room.message'
+                    AND c.state_key = e.sender
+            """
+            txn.execute(sql, (room_id,))
+            return [r[0] for r in txn]
+
+        return await self.db_pool.runInteraction(
+            "_get_participants_in_room_txn", _get_participants_in_room_txn, room_id
+        )
+
 
 class RoomMemberBackgroundUpdateStore(SQLBaseStore):
     def __init__(
diff --git a/tests/rest/admin/test_room.py b/tests/rest/admin/test_room.py
index 95ed7364510..617c15071a3 100644
--- a/tests/rest/admin/test_room.py
+++ b/tests/rest/admin/test_room.py
@@ -2018,6 +2018,82 @@ def test_room_members(self) -> None:
         )
         self.assertEqual(channel.json_body["total"], 3)
 
+    def test_room_members_participants_param(self) -> None:
+        """
+        Test that /_synapse/admin/v1/rooms/{room_id}/members with a query param value of
+        participant=true returns a list of currently joined users who have posted, and
+        that the list does not contain room members who have not posted
+        """
+
+        participant = self.register_user("participant", "pass")
+        participant_tok = self.login("participant", "pass")
+        room_id = self.helper.create_room_as(participant, tok=participant_tok)
+
+        participant2 = self.register_user("participant2", "pass")
+        participant2_tok = self.login("participant2", "pass")
+        self.helper.join(room_id, participant2, tok=participant2_tok)
+
+        # have some lurkers join the room
+        for i in range(5):
+            user = self.register_user(f"user{i}", "pass")
+            user_tok = self.login(f"user{i}", "pass")
+            self.helper.join(room_id, user, tok=user_tok)
+
+        # double-check the room membership total, should be 7
+        channel = self.make_request(
+            "GET",
+            f"/_synapse/admin/v1/rooms/{room_id}/members",
+            access_token=self.admin_user_tok,
+        )
+        self.assertEqual(200, channel.code)
+        self.assertEqual(channel.json_body["total"], 7)
+
+        # participants send messages
+        self.helper.send_event(
+            room_id,
+            "m.room.message",
+            content={
+                "msgtype": "m.text",
+                "body": "nefarious activity",
+            },
+            tok=participant_tok,
+        )
+
+        self.helper.send_event(
+            room_id,
+            "m.room.message",
+            content={
+                "msgtype": "m.text",
+                "body": "more nefarious activity",
+            },
+            tok=participant2_tok,
+        )
+
+        channel = self.make_request(
+            "GET",
+            f"/_synapse/admin/v1/rooms/{room_id}/members?participant=true",
+            access_token=self.admin_user_tok,
+        )
+        self.assertEqual(200, channel.code)
+        participants = channel.json_body["members"]
+        self.assertEqual(channel.json_body["total"], 2)
+        self.assertIn(participant, participants)
+        self.assertIn(participant2, participants)
+
+        # have participants leave room
+        self.helper.leave(room_id, participant, tok=participant_tok)
+        self.helper.leave(room_id, participant2, tok=participant2_tok)
+
+        # there should no longer be any active participants
+        channel = self.make_request(
+            "GET",
+            f"/_synapse/admin/v1/rooms/{room_id}/members?participant=true",
+            access_token=self.admin_user_tok,
+        )
+        self.assertEqual(200, channel.code)
+        participants = channel.json_body["total"]
+        self.assertEqual(participants, 0)
+
     def test_room_state(self) -> None:
         """Test that room state can be requested correctly"""
         # Create two test rooms