diff --git a/changelog.d/6666.misc b/changelog.d/6666.misc
new file mode 100644
index 0000000000..e79c23d2d2
--- /dev/null
+++ b/changelog.d/6666.misc
@@ -0,0 +1 @@
+Port `synapse.replication.tcp` to async/await.
diff --git a/synapse/app/admin_cmd.py b/synapse/app/admin_cmd.py
index 8e36bc57d3..1c7c6ec0c8 100644
--- a/synapse/app/admin_cmd.py
+++ b/synapse/app/admin_cmd.py
@@ -84,8 +84,7 @@ class AdminCmdServer(HomeServer):
 
 
 class AdminCmdReplicationHandler(ReplicationClientHandler):
-    @defer.inlineCallbacks
-    def on_rdata(self, stream_name, token, rows):
+    async def on_rdata(self, stream_name, token, rows):
         pass
 
     def get_streams_to_replicate(self):
diff --git a/synapse/app/appservice.py b/synapse/app/appservice.py
index e82e0f11e3..2217d4a4fb 100644
--- a/synapse/app/appservice.py
+++ b/synapse/app/appservice.py
@@ -115,9 +115,8 @@ class ASReplicationHandler(ReplicationClientHandler):
         super(ASReplicationHandler, self).__init__(hs.get_datastore())
         self.appservice_handler = hs.get_application_service_handler()
 
-    @defer.inlineCallbacks
-    def on_rdata(self, stream_name, token, rows):
-        yield super(ASReplicationHandler, self).on_rdata(stream_name, token, rows)
+    async def on_rdata(self, stream_name, token, rows):
+        await super(ASReplicationHandler, self).on_rdata(stream_name, token, rows)
 
         if stream_name == "events":
             max_stream_id = self.store.get_room_max_stream_ordering()
diff --git a/synapse/app/federation_sender.py b/synapse/app/federation_sender.py
index 83c436229c..a57cf991ac 100644
--- a/synapse/app/federation_sender.py
+++ b/synapse/app/federation_sender.py
@@ -145,9 +145,8 @@ class FederationSenderReplicationHandler(ReplicationClientHandler):
         super(FederationSenderReplicationHandler, self).__init__(hs.get_datastore())
         self.send_handler = FederationSenderHandler(hs, self)
 
-    @defer.inlineCallbacks
-    def on_rdata(self, stream_name, token, rows):
-        yield super(FederationSenderReplicationHandler, self).on_rdata(
+    async def on_rdata(self, stream_name, token, rows):
+        await super(FederationSenderReplicationHandler, self).on_rdata(
             stream_name, token, rows
         )
         self.send_handler.process_replication_rows(stream_name, token, rows)
diff --git a/synapse/app/pusher.py b/synapse/app/pusher.py
index 09e639040a..e46b6ac598 100644
--- a/synapse/app/pusher.py
+++ b/synapse/app/pusher.py
@@ -141,9 +141,8 @@ class PusherReplicationHandler(ReplicationClientHandler):
 
         self.pusher_pool = hs.get_pusherpool()
 
-    @defer.inlineCallbacks
-    def on_rdata(self, stream_name, token, rows):
-        yield super(PusherReplicationHandler, self).on_rdata(stream_name, token, rows)
+    async def on_rdata(self, stream_name, token, rows):
+        await super(PusherReplicationHandler, self).on_rdata(stream_name, token, rows)
         run_in_background(self.poke_pushers, stream_name, token, rows)
 
     @defer.inlineCallbacks
diff --git a/synapse/app/synchrotron.py b/synapse/app/synchrotron.py
index 03031ee34d..3218da07bd 100644
--- a/synapse/app/synchrotron.py
+++ b/synapse/app/synchrotron.py
@@ -358,9 +358,8 @@ class SyncReplicationHandler(ReplicationClientHandler):
         self.presence_handler = hs.get_presence_handler()
         self.notifier = hs.get_notifier()
 
-    @defer.inlineCallbacks
-    def on_rdata(self, stream_name, token, rows):
-        yield super(SyncReplicationHandler, self).on_rdata(stream_name, token, rows)
+    async def on_rdata(self, stream_name, token, rows):
+        await super(SyncReplicationHandler, self).on_rdata(stream_name, token, rows)
         run_in_background(self.process_and_notify, stream_name, token, rows)
 
     def get_streams_to_replicate(self):
diff --git a/synapse/app/user_dir.py b/synapse/app/user_dir.py
index 1257098f92..ba536d6f04 100644
--- a/synapse/app/user_dir.py
+++ b/synapse/app/user_dir.py
@@ -172,9 +172,8 @@ class UserDirectoryReplicationHandler(ReplicationClientHandler):
         super(UserDirectoryReplicationHandler, self).__init__(hs.get_datastore())
         self.user_directory = hs.get_user_directory_handler()
 
-    @defer.inlineCallbacks
-    def on_rdata(self, stream_name, token, rows):
-        yield super(UserDirectoryReplicationHandler, self).on_rdata(
+    async def on_rdata(self, stream_name, token, rows):
+        await super(UserDirectoryReplicationHandler, self).on_rdata(
             stream_name, token, rows
         )
         if stream_name == EventsStream.NAME:
diff --git a/synapse/federation/send_queue.py b/synapse/federation/send_queue.py
index ced4925a98..174f6e42be 100644
--- a/synapse/federation/send_queue.py
+++ b/synapse/federation/send_queue.py
@@ -259,7 +259,9 @@ class FederationRemoteSendQueue(object):
     def federation_ack(self, token):
         self._clear_queue_before_pos(token)
 
-    def get_replication_rows(self, from_token, to_token, limit, federation_ack=None):
+    async def get_replication_rows(
+        self, from_token, to_token, limit, federation_ack=None
+    ):
         """Get rows to be sent over federation between the two tokens
 
         Args:
diff --git a/synapse/handlers/typing.py b/synapse/handlers/typing.py
index b635c339ed..d5ca9cb07b 100644
--- a/synapse/handlers/typing.py
+++ b/synapse/handlers/typing.py
@@ -257,7 +257,7 @@ class TypingHandler(object):
             "typing_key", self._latest_room_serial, rooms=[member.room_id]
         )
 
-    def get_all_typing_updates(self, last_id, current_id):
+    async def get_all_typing_updates(self, last_id, current_id):
         if last_id == current_id:
             return []
 
diff --git a/synapse/replication/tcp/client.py b/synapse/replication/tcp/client.py
index aa7fd90e26..52a0aefe68 100644
--- a/synapse/replication/tcp/client.py
+++ b/synapse/replication/tcp/client.py
@@ -110,7 +110,7 @@ class ReplicationClientHandler(AbstractReplicationClientHandler):
         port = hs.config.worker_replication_port
         hs.get_reactor().connectTCP(host, port, self.factory)
 
-    def on_rdata(self, stream_name, token, rows):
+    async def on_rdata(self, stream_name, token, rows):
         """Called to handle a batch of replication data with a given stream token.
 
         By default this just pokes the slave store. Can be overridden in subclasses to
@@ -121,20 +121,17 @@ class ReplicationClientHandler(AbstractReplicationClientHandler):
             token (int): stream token for this batch of rows
             rows (list): a list of Stream.ROW_TYPE objects as returned by
                 Stream.parse_row.
-
-        Returns:
-            Deferred|None
         """
         logger.debug("Received rdata %s -> %s", stream_name, token)
-        return self.store.process_replication_rows(stream_name, token, rows)
+        self.store.process_replication_rows(stream_name, token, rows)
 
-    def on_position(self, stream_name, token):
+    async def on_position(self, stream_name, token):
         """Called when we get new position data. By default this just pokes
         the slave store.
 
         Can be overriden in subclasses to handle more.
         """
-        return self.store.process_replication_rows(stream_name, token, [])
+        self.store.process_replication_rows(stream_name, token, [])
 
     def on_sync(self, data):
         """When we received a SYNC we wake up any deferreds that were waiting
diff --git a/synapse/replication/tcp/protocol.py b/synapse/replication/tcp/protocol.py
index db0353c996..5f4bdf84d2 100644
--- a/synapse/replication/tcp/protocol.py
+++ b/synapse/replication/tcp/protocol.py
@@ -81,12 +81,11 @@ from synapse.replication.tcp.commands import (
     SyncCommand,
     UserSyncCommand,
 )
+from synapse.replication.tcp.streams import STREAMS_MAP
 from synapse.types import Collection
 from synapse.util import Clock
 from synapse.util.stringutils import random_string
 
-from .streams import STREAMS_MAP
-
 connection_close_counter = Counter(
     "synapse_replication_tcp_protocol_close_reason", "", ["reason_type"]
 )
@@ -241,19 +240,16 @@ class BaseReplicationStreamProtocol(LineOnlyReceiver):
             "replication-" + cmd.get_logcontext_id(), self.handle_command, cmd
         )
 
-    def handle_command(self, cmd):
+    async def handle_command(self, cmd: Command):
         """Handle a command we have received over the replication stream.
 
-        By default delegates to on_<COMMAND>
+        By default delegates to on_<COMMAND>, which should return an awaitable.
 
         Args:
-            cmd (synapse.replication.tcp.commands.Command): received command
-
-        Returns:
-            Deferred
+            cmd: received command
         """
         handler = getattr(self, "on_%s" % (cmd.NAME,))
-        return handler(cmd)
+        await handler(cmd)
 
     def close(self):
         logger.warning("[%s] Closing connection", self.id())
@@ -326,10 +322,10 @@ class BaseReplicationStreamProtocol(LineOnlyReceiver):
         for cmd in pending:
             self.send_command(cmd)
 
-    def on_PING(self, line):
+    async def on_PING(self, line):
         self.received_ping = True
 
-    def on_ERROR(self, cmd):
+    async def on_ERROR(self, cmd):
         logger.error("[%s] Remote reported error: %r", self.id(), cmd.data)
 
     def pauseProducing(self):
@@ -429,16 +425,16 @@ class ServerReplicationStreamProtocol(BaseReplicationStreamProtocol):
         BaseReplicationStreamProtocol.connectionMade(self)
         self.streamer.new_connection(self)
 
-    def on_NAME(self, cmd):
+    async def on_NAME(self, cmd):
         logger.info("[%s] Renamed to %r", self.id(), cmd.data)
         self.name = cmd.data
 
-    def on_USER_SYNC(self, cmd):
-        return self.streamer.on_user_sync(
+    async def on_USER_SYNC(self, cmd):
+        await self.streamer.on_user_sync(
             self.conn_id, cmd.user_id, cmd.is_syncing, cmd.last_sync_ms
         )
 
-    def on_REPLICATE(self, cmd):
+    async def on_REPLICATE(self, cmd):
         stream_name = cmd.stream_name
         token = cmd.token
 
@@ -449,23 +445,23 @@ class ServerReplicationStreamProtocol(BaseReplicationStreamProtocol):
                 for stream in iterkeys(self.streamer.streams_by_name)
             ]
 
-            return make_deferred_yieldable(
+            await make_deferred_yieldable(
                 defer.gatherResults(deferreds, consumeErrors=True)
             )
         else:
-            return self.subscribe_to_stream(stream_name, token)
+            await self.subscribe_to_stream(stream_name, token)
 
-    def on_FEDERATION_ACK(self, cmd):
-        return self.streamer.federation_ack(cmd.token)
+    async def on_FEDERATION_ACK(self, cmd):
+        self.streamer.federation_ack(cmd.token)
 
-    def on_REMOVE_PUSHER(self, cmd):
-        return self.streamer.on_remove_pusher(cmd.app_id, cmd.push_key, cmd.user_id)
+    async def on_REMOVE_PUSHER(self, cmd):
+        await self.streamer.on_remove_pusher(cmd.app_id, cmd.push_key, cmd.user_id)
 
-    def on_INVALIDATE_CACHE(self, cmd):
-        return self.streamer.on_invalidate_cache(cmd.cache_func, cmd.keys)
+    async def on_INVALIDATE_CACHE(self, cmd):
+        self.streamer.on_invalidate_cache(cmd.cache_func, cmd.keys)
 
-    def on_USER_IP(self, cmd):
-        return self.streamer.on_user_ip(
+    async def on_USER_IP(self, cmd):
+        self.streamer.on_user_ip(
             cmd.user_id,
             cmd.access_token,
             cmd.ip,
@@ -474,8 +470,7 @@ class ServerReplicationStreamProtocol(BaseReplicationStreamProtocol):
             cmd.last_seen,
         )
 
-    @defer.inlineCallbacks
-    def subscribe_to_stream(self, stream_name, token):
+    async def subscribe_to_stream(self, stream_name, token):
         """Subscribe the remote to a stream.
 
         This invloves checking if they've missed anything and sending those
@@ -487,7 +482,7 @@ class ServerReplicationStreamProtocol(BaseReplicationStreamProtocol):
 
         try:
             # Get missing updates
-            updates, current_token = yield self.streamer.get_stream_updates(
+            updates, current_token = await self.streamer.get_stream_updates(
                 stream_name, token
             )
 
@@ -572,7 +567,7 @@ class AbstractReplicationClientHandler(metaclass=abc.ABCMeta):
     """
 
     @abc.abstractmethod
-    def on_rdata(self, stream_name, token, rows):
+    async def on_rdata(self, stream_name, token, rows):
         """Called to handle a batch of replication data with a given stream token.
 
         Args:
@@ -580,14 +575,11 @@ class AbstractReplicationClientHandler(metaclass=abc.ABCMeta):
             token (int): stream token for this batch of rows
             rows (list): a list of Stream.ROW_TYPE objects as returned by
                 Stream.parse_row.
-
-        Returns:
-            Deferred|None
         """
         raise NotImplementedError()
 
     @abc.abstractmethod
-    def on_position(self, stream_name, token):
+    async def on_position(self, stream_name, token):
         """Called when we get new position data."""
         raise NotImplementedError()
 
@@ -676,12 +668,12 @@ class ClientReplicationStreamProtocol(BaseReplicationStreamProtocol):
         if not self.streams_connecting:
             self.handler.finished_connecting()
 
-    def on_SERVER(self, cmd):
+    async def on_SERVER(self, cmd):
         if cmd.data != self.server_name:
             logger.error("[%s] Connected to wrong remote: %r", self.id(), cmd.data)
             self.send_error("Wrong remote")
 
-    def on_RDATA(self, cmd):
+    async def on_RDATA(self, cmd):
         stream_name = cmd.stream_name
         inbound_rdata_count.labels(stream_name).inc()
 
@@ -701,19 +693,19 @@ class ClientReplicationStreamProtocol(BaseReplicationStreamProtocol):
             # Check if this is the last of a batch of updates
             rows = self.pending_batches.pop(stream_name, [])
             rows.append(row)
-            return self.handler.on_rdata(stream_name, cmd.token, rows)
+            await self.handler.on_rdata(stream_name, cmd.token, rows)
 
-    def on_POSITION(self, cmd):
+    async def on_POSITION(self, cmd):
         # When we get a `POSITION` command it means we've finished getting
         # missing updates for the given stream, and are now up to date.
         self.streams_connecting.discard(cmd.stream_name)
         if not self.streams_connecting:
             self.handler.finished_connecting()
 
-        return self.handler.on_position(cmd.stream_name, cmd.token)
+        await self.handler.on_position(cmd.stream_name, cmd.token)
 
-    def on_SYNC(self, cmd):
-        return self.handler.on_sync(cmd.data)
+    async def on_SYNC(self, cmd):
+        self.handler.on_sync(cmd.data)
 
     def replicate(self, stream_name, token):
         """Send the subscription request to the server
diff --git a/synapse/replication/tcp/resource.py b/synapse/replication/tcp/resource.py
index cbfdaf5773..b1752e88cd 100644
--- a/synapse/replication/tcp/resource.py
+++ b/synapse/replication/tcp/resource.py
@@ -23,7 +23,6 @@ from six import itervalues
 
 from prometheus_client import Counter
 
-from twisted.internet import defer
 from twisted.internet.protocol import Factory
 
 from synapse.metrics import LaterGauge
@@ -155,8 +154,7 @@ class ReplicationStreamer(object):
 
         run_as_background_process("replication_notifier", self._run_notifier_loop)
 
-    @defer.inlineCallbacks
-    def _run_notifier_loop(self):
+    async def _run_notifier_loop(self):
         self.is_looping = True
 
         try:
@@ -185,7 +183,7 @@ class ReplicationStreamer(object):
                             continue
 
                         if self._replication_torture_level:
-                            yield self.clock.sleep(
+                            await self.clock.sleep(
                                 self._replication_torture_level / 1000.0
                             )
 
@@ -196,7 +194,7 @@ class ReplicationStreamer(object):
                             stream.upto_token,
                         )
                         try:
-                            updates, current_token = yield stream.get_updates()
+                            updates, current_token = await stream.get_updates()
                         except Exception:
                             logger.info("Failed to handle stream %s", stream.NAME)
                             raise
@@ -233,7 +231,7 @@ class ReplicationStreamer(object):
             self.is_looping = False
 
     @measure_func("repl.get_stream_updates")
-    def get_stream_updates(self, stream_name, token):
+    async def get_stream_updates(self, stream_name, token):
         """For a given stream get all updates since token. This is called when
         a client first subscribes to a stream.
         """
@@ -241,7 +239,7 @@ class ReplicationStreamer(object):
         if not stream:
             raise Exception("unknown stream %s", stream_name)
 
-        return stream.get_updates_since(token)
+        return await stream.get_updates_since(token)
 
     @measure_func("repl.federation_ack")
     def federation_ack(self, token):
@@ -252,22 +250,20 @@ class ReplicationStreamer(object):
             self.federation_sender.federation_ack(token)
 
     @measure_func("repl.on_user_sync")
-    @defer.inlineCallbacks
-    def on_user_sync(self, conn_id, user_id, is_syncing, last_sync_ms):
+    async def on_user_sync(self, conn_id, user_id, is_syncing, last_sync_ms):
         """A client has started/stopped syncing on a worker.
         """
         user_sync_counter.inc()
-        yield self.presence_handler.update_external_syncs_row(
+        await self.presence_handler.update_external_syncs_row(
             conn_id, user_id, is_syncing, last_sync_ms
         )
 
     @measure_func("repl.on_remove_pusher")
-    @defer.inlineCallbacks
-    def on_remove_pusher(self, app_id, push_key, user_id):
+    async def on_remove_pusher(self, app_id, push_key, user_id):
         """A client has asked us to remove a pusher
         """
         remove_pusher_counter.inc()
-        yield self.store.delete_pusher_by_app_id_pushkey_user_id(
+        await self.store.delete_pusher_by_app_id_pushkey_user_id(
             app_id=app_id, pushkey=push_key, user_id=user_id
         )
 
@@ -281,15 +277,16 @@ class ReplicationStreamer(object):
         getattr(self.store, cache_func).invalidate(tuple(keys))
 
     @measure_func("repl.on_user_ip")
-    @defer.inlineCallbacks
-    def on_user_ip(self, user_id, access_token, ip, user_agent, device_id, last_seen):
+    async def on_user_ip(
+        self, user_id, access_token, ip, user_agent, device_id, last_seen
+    ):
         """The client saw a user request
         """
         user_ip_cache_counter.inc()
-        yield self.store.insert_client_ip(
+        await self.store.insert_client_ip(
             user_id, access_token, ip, user_agent, device_id, last_seen
         )
-        yield self._server_notices_sender.on_user_ip(user_id)
+        await self._server_notices_sender.on_user_ip(user_id)
 
     def send_sync_to_all_connections(self, data):
         """Sends a SYNC command to all clients.
diff --git a/synapse/replication/tcp/streams/_base.py b/synapse/replication/tcp/streams/_base.py
index 4ab0334fc1..e03e77199b 100644
--- a/synapse/replication/tcp/streams/_base.py
+++ b/synapse/replication/tcp/streams/_base.py
@@ -19,8 +19,6 @@ import logging
 from collections import namedtuple
 from typing import Any
 
-from twisted.internet import defer
-
 logger = logging.getLogger(__name__)
 
 
@@ -144,8 +142,7 @@ class Stream(object):
         self.upto_token = self.current_token()
         self.last_token = self.upto_token
 
-    @defer.inlineCallbacks
-    def get_updates(self):
+    async def get_updates(self):
         """Gets all updates since the last time this function was called (or
         since the stream was constructed if it hadn't been called before),
         until the `upto_token`
@@ -156,13 +153,12 @@ class Stream(object):
                 list of ``(token, row)`` entries. ``row`` will be json-serialised and
                 sent over the replication steam.
         """
-        updates, current_token = yield self.get_updates_since(self.last_token)
+        updates, current_token = await self.get_updates_since(self.last_token)
         self.last_token = current_token
 
         return updates, current_token
 
-    @defer.inlineCallbacks
-    def get_updates_since(self, from_token):
+    async def get_updates_since(self, from_token):
         """Like get_updates except allows specifying from when we should
         stream updates
 
@@ -182,15 +178,16 @@ class Stream(object):
         if from_token == current_token:
             return [], current_token
 
+        logger.info("get_updates_since: %s", self.__class__)
         if self._LIMITED:
-            rows = yield self.update_function(
+            rows = await self.update_function(
                 from_token, current_token, limit=MAX_EVENTS_BEHIND + 1
             )
 
             # never turn more than MAX_EVENTS_BEHIND + 1 into updates.
             rows = itertools.islice(rows, MAX_EVENTS_BEHIND + 1)
         else:
-            rows = yield self.update_function(from_token, current_token)
+            rows = await self.update_function(from_token, current_token)
 
         updates = [(row[0], row[1:]) for row in rows]
 
@@ -295,9 +292,8 @@ class PushRulesStream(Stream):
         push_rules_token, _ = self.store.get_push_rules_stream_token()
         return push_rules_token
 
-    @defer.inlineCallbacks
-    def update_function(self, from_token, to_token, limit):
-        rows = yield self.store.get_all_push_rule_updates(from_token, to_token, limit)
+    async def update_function(self, from_token, to_token, limit):
+        rows = await self.store.get_all_push_rule_updates(from_token, to_token, limit)
         return [(row[0], row[2]) for row in rows]
 
 
@@ -413,9 +409,8 @@ class AccountDataStream(Stream):
 
         super(AccountDataStream, self).__init__(hs)
 
-    @defer.inlineCallbacks
-    def update_function(self, from_token, to_token, limit):
-        global_results, room_results = yield self.store.get_all_updated_account_data(
+    async def update_function(self, from_token, to_token, limit):
+        global_results, room_results = await self.store.get_all_updated_account_data(
             from_token, from_token, to_token, limit
         )
 
diff --git a/synapse/replication/tcp/streams/events.py b/synapse/replication/tcp/streams/events.py
index 0843e5aa90..b3afabb8cd 100644
--- a/synapse/replication/tcp/streams/events.py
+++ b/synapse/replication/tcp/streams/events.py
@@ -19,8 +19,6 @@ from typing import Tuple, Type
 
 import attr
 
-from twisted.internet import defer
-
 from ._base import Stream
 
 
@@ -122,16 +120,15 @@ class EventsStream(Stream):
 
         super(EventsStream, self).__init__(hs)
 
-    @defer.inlineCallbacks
-    def update_function(self, from_token, current_token, limit=None):
-        event_rows = yield self._store.get_all_new_forward_event_rows(
+    async def update_function(self, from_token, current_token, limit=None):
+        event_rows = await self._store.get_all_new_forward_event_rows(
             from_token, current_token, limit
         )
         event_updates = (
             (row[0], EventsStreamEventRow.TypeId, row[1:]) for row in event_rows
         )
 
-        state_rows = yield self._store.get_all_updated_current_state_deltas(
+        state_rows = await self._store.get_all_updated_current_state_deltas(
             from_token, current_token, limit
         )
         state_updates = (
diff --git a/tests/replication/tcp/streams/_base.py b/tests/replication/tcp/streams/_base.py
index 1d14e77255..e96ad4ca4e 100644
--- a/tests/replication/tcp/streams/_base.py
+++ b/tests/replication/tcp/streams/_base.py
@@ -73,6 +73,6 @@ class TestReplicationClientHandler(object):
     def finished_connecting(self):
         pass
 
-    def on_rdata(self, stream_name, token, rows):
+    async def on_rdata(self, stream_name, token, rows):
         for r in rows:
             self.received_rdata_rows.append((stream_name, token, r))