diff --git a/chit_chat/viewsets.py b/chit_chat/viewsets.py
index 60e0563..0f64db9 100644
--- a/chit_chat/viewsets.py
+++ b/chit_chat/viewsets.py
@@ -1,5 +1,7 @@
 from rest_framework import viewsets, mixins
 from django.db.models import Max
+from rest_framework.decorators import action
+from rest_framework.response import Response
 
 from chit_chat.models import Room
 from chit_chat.serializers import RoomSerializer
@@ -22,3 +24,9 @@ def get_queryset(self):
             'members',
         )
         return qs
+
+    @action(methods=['post'], detail=True)
+    def viewed_all_messages(self, request, pk, *args, **kwargs):
+        room = self.get_object()
+        request.user.chat_room_messages_viewed.set(room.messages.all())
+        return Response()
diff --git a/tests/integration/test_chat.py b/tests/integration/test_chat.py
index e8d2973..086188b 100644
--- a/tests/integration/test_chat.py
+++ b/tests/integration/test_chat.py
@@ -83,3 +83,18 @@ def test_rooms_are_ordered_by_latest_message(self):
         data = resp.json()['results']
         assert data[0]['id'] == room_1.pk
         assert data[1]['id'] == room_2.pk
+
+    def test_mark_all_messages_in_room_as_viewed(self):
+        room_1 = RoomFactory(members=[self.user])
+        message_1 = MessageFactory(room=room_1)
+        room_2 = RoomFactory(members=[self.user])
+        message_2 = MessageFactory(room=room_2)
+
+        assert not message_1.users_who_viewed.filter(pk=self.user.pk).exists()
+        assert not message_2.users_who_viewed.filter(pk=self.user.pk).exists()
+
+        resp = self.client.post(reverse('room-viewed-all-messages', args=(room_1.pk,)))
+        assert resp.status_code == 200
+
+        assert message_1.users_who_viewed.filter(pk=self.user.pk).exists()
+        assert not message_2.users_who_viewed.filter(pk=self.user.pk).exists()