diff --git a/homeassistant/components/harmony/data.py b/homeassistant/components/harmony/data.py
index 8c1d137bc85..340596ff1ef 100644
--- a/homeassistant/components/harmony/data.py
+++ b/homeassistant/components/harmony/data.py
@@ -22,17 +22,8 @@ class HarmonyData(HarmonySubscriberMixin):
         self._name = name
         self._unique_id = unique_id
         self._available = False
-
-        callbacks = {
-            "config_updated": self._config_updated,
-            "connect": self._connected,
-            "disconnect": self._disconnected,
-            "new_activity_starting": self._activity_starting,
-            "new_activity": self._activity_started,
-        }
-        self._client = HarmonyClient(
-            ip_address=address, callbacks=ClientCallbackType(**callbacks)
-        )
+        self._client = None
+        self._address = address
 
     @property
     def activities(self):
@@ -105,6 +96,18 @@ class HarmonyData(HarmonySubscriberMixin):
     async def connect(self) -> bool:
         """Connect to the Harmony Hub."""
         _LOGGER.debug("%s: Connecting", self._name)
+
+        callbacks = {
+            "config_updated": self._config_updated,
+            "connect": self._connected,
+            "disconnect": self._disconnected,
+            "new_activity_starting": self._activity_starting,
+            "new_activity": self._activity_started,
+        }
+        self._client = HarmonyClient(
+            ip_address=self._address, callbacks=ClientCallbackType(**callbacks)
+        )
+
         try:
             if not await self._client.connect():
                 _LOGGER.warning("%s: Unable to connect to HUB", self._name)
@@ -113,6 +116,7 @@ class HarmonyData(HarmonySubscriberMixin):
         except aioexc.TimeOut:
             _LOGGER.warning("%s: Connection timed-out", self._name)
             return False
+
         return True
 
     async def shutdown(self):
@@ -159,10 +163,12 @@ class HarmonyData(HarmonySubscriberMixin):
             )
             return
 
+        await self.async_lock_start_activity()
         try:
             await self._client.start_activity(activity_id)
         except aioexc.TimeOut:
             _LOGGER.error("%s: Starting activity %s timed-out", self.name, activity)
+            self.async_unlock_start_activity()
 
     async def async_power_off(self):
         """Start the PowerOff activity."""
diff --git a/homeassistant/components/harmony/subscriber.py b/homeassistant/components/harmony/subscriber.py
index d3bed33d560..b2652cc43d1 100644
--- a/homeassistant/components/harmony/subscriber.py
+++ b/homeassistant/components/harmony/subscriber.py
@@ -1,5 +1,6 @@
 """Mixin class for handling harmony callback subscriptions."""
 
+import asyncio
 import logging
 from typing import Any, Callable, NamedTuple, Optional
 
@@ -29,6 +30,17 @@ class HarmonySubscriberMixin:
         super().__init__()
         self._hass = hass
         self._subscriptions = []
+        self._activity_lock = asyncio.Lock()
+
+    async def async_lock_start_activity(self):
+        """Acquire the lock."""
+        await self._activity_lock.acquire()
+
+    @callback
+    def async_unlock_start_activity(self):
+        """Release the lock."""
+        if self._activity_lock.locked():
+            self._activity_lock.release()
 
     @callback
     def async_subscribe(self, update_callbacks: HarmonyCallback) -> Callable:
@@ -51,11 +63,13 @@ class HarmonySubscriberMixin:
 
     def _connected(self, _=None) -> None:
         _LOGGER.debug("connected")
+        self.async_unlock_start_activity()
         self._available = True
         self._call_callbacks("connected")
 
     def _disconnected(self, _=None) -> None:
         _LOGGER.debug("disconnected")
+        self.async_unlock_start_activity()
         self._available = False
         self._call_callbacks("disconnected")
 
@@ -65,6 +79,7 @@ class HarmonySubscriberMixin:
 
     def _activity_started(self, activity_info: tuple) -> None:
         _LOGGER.debug("activity %s started", activity_info)
+        self.async_unlock_start_activity()
         self._call_callbacks("activity_started", activity_info)
 
     def _call_callbacks(self, callback_func_name: str, argument: tuple = None):