diff --git a/homeassistant/components/mqtt/const.py b/homeassistant/components/mqtt/const.py
index 6c334eca311..6435670e92c 100644
--- a/homeassistant/components/mqtt/const.py
+++ b/homeassistant/components/mqtt/const.py
@@ -9,11 +9,13 @@ ATTR_QOS = "qos"
 ATTR_RETAIN = "retain"
 ATTR_TOPIC = "topic"
 
+CONF_AVAILABILITY = "availability"
 CONF_BROKER = "broker"
 CONF_BIRTH_MESSAGE = "birth_message"
 CONF_QOS = ATTR_QOS
 CONF_RETAIN = ATTR_RETAIN
 CONF_STATE_TOPIC = "state_topic"
+CONF_TOPIC = "topic"
 CONF_WILL_MESSAGE = "will_message"
 
 DATA_MQTT_CONFIG = "mqtt_config"
diff --git a/homeassistant/components/mqtt/discovery.py b/homeassistant/components/mqtt/discovery.py
index 6996072d226..5678f31f5b2 100644
--- a/homeassistant/components/mqtt/discovery.py
+++ b/homeassistant/components/mqtt/discovery.py
@@ -22,6 +22,8 @@ from .const import (
     ATTR_DISCOVERY_HASH,
     ATTR_DISCOVERY_PAYLOAD,
     ATTR_DISCOVERY_TOPIC,
+    CONF_AVAILABILITY,
+    CONF_TOPIC,
     DOMAIN,
 )
 
@@ -138,6 +140,14 @@ async def async_start(  # noqa: C901
                         payload[key] = f"{base}{value[1:]}"
                     if value[-1] == TOPIC_BASE and key.endswith("topic"):
                         payload[key] = f"{value[:-1]}{base}"
+            if payload.get(CONF_AVAILABILITY):
+                for availability_conf in payload[CONF_AVAILABILITY]:
+                    topic = availability_conf.get(CONF_TOPIC)
+                    if topic:
+                        if topic[0] == TOPIC_BASE:
+                            availability_conf[CONF_TOPIC] = f"{base}{topic[1:]}"
+                        if topic[-1] == TOPIC_BASE:
+                            availability_conf[CONF_TOPIC] = f"{topic[:-1]}{base}"
 
         # If present, the node_id will be included in the discovered object id
         discovery_id = " ".join((node_id, object_id)) if node_id else object_id
diff --git a/homeassistant/components/mqtt/mixins.py b/homeassistant/components/mqtt/mixins.py
index e21f3f5c280..6c29938c75d 100644
--- a/homeassistant/components/mqtt/mixins.py
+++ b/homeassistant/components/mqtt/mixins.py
@@ -18,12 +18,14 @@ from homeassistant.helpers.dispatcher import (
 from homeassistant.helpers.entity import Entity
 from homeassistant.helpers.typing import ConfigType
 
-from . import CONF_TOPIC, DATA_MQTT, debug_info, publish, subscription
+from . import DATA_MQTT, debug_info, publish, subscription
 from .const import (
     ATTR_DISCOVERY_HASH,
     ATTR_DISCOVERY_PAYLOAD,
     ATTR_DISCOVERY_TOPIC,
+    CONF_AVAILABILITY,
     CONF_QOS,
+    CONF_TOPIC,
     DEFAULT_PAYLOAD_AVAILABLE,
     DEFAULT_PAYLOAD_NOT_AVAILABLE,
     DOMAIN,
@@ -50,7 +52,6 @@ AVAILABILITY_LATEST = "latest"
 
 AVAILABILITY_MODES = [AVAILABILITY_ALL, AVAILABILITY_ANY, AVAILABILITY_LATEST]
 
-CONF_AVAILABILITY = "availability"
 CONF_AVAILABILITY_MODE = "availability_mode"
 CONF_AVAILABILITY_TOPIC = "availability_topic"
 CONF_ENABLED_BY_DEFAULT = "enabled_by_default"
@@ -108,7 +109,7 @@ MQTT_AVAILABILITY_LIST_SCHEMA = vol.Schema(
             cv.ensure_list,
             [
                 {
-                    vol.Optional(CONF_TOPIC): valid_subscribe_topic,
+                    vol.Required(CONF_TOPIC): valid_subscribe_topic,
                     vol.Optional(
                         CONF_PAYLOAD_AVAILABLE, default=DEFAULT_PAYLOAD_AVAILABLE
                     ): cv.string,
diff --git a/tests/components/mqtt/test_discovery.py b/tests/components/mqtt/test_discovery.py
index 907c3d398b6..8d2106c90fa 100644
--- a/tests/components/mqtt/test_discovery.py
+++ b/tests/components/mqtt/test_discovery.py
@@ -12,7 +12,12 @@ from homeassistant.components.mqtt.abbreviations import (
     DEVICE_ABBREVIATIONS,
 )
 from homeassistant.components.mqtt.discovery import ALREADY_DISCOVERED, async_start
-from homeassistant.const import EVENT_STATE_CHANGED, STATE_OFF, STATE_ON
+from homeassistant.const import (
+    EVENT_STATE_CHANGED,
+    STATE_OFF,
+    STATE_ON,
+    STATE_UNAVAILABLE,
+)
 import homeassistant.core as ha
 
 from tests.common import (
@@ -449,6 +454,18 @@ async def test_discovery_expansion(hass, mqtt_mock, caplog):
         '  "name": "DiscoveryExpansionTest1",'
         '  "stat_t": "test_topic/~",'
         '  "cmd_t": "~/test_topic",'
+        '  "availability": ['
+        "    {"
+        '      "topic":"~/avail_item1",'
+        '      "payload_available": "available",'
+        '      "payload_not_available": "not_available"'
+        "    },"
+        "    {"
+        '      "topic":"avail_item2/~",'
+        '      "payload_available": "available",'
+        '      "payload_not_available": "not_available"'
+        "    }"
+        "  ],"
         '  "dev":{'
         '    "ids":["5706DF"],'
         '    "name":"DiscoveryExpansionTest1 Device",'
@@ -463,6 +480,12 @@ async def test_discovery_expansion(hass, mqtt_mock, caplog):
     async_fire_mqtt_message(hass, "homeassistant/switch/bla/config", data)
     await hass.async_block_till_done()
 
+    state = hass.states.get("switch.DiscoveryExpansionTest1")
+    assert state.state == STATE_UNAVAILABLE
+
+    async_fire_mqtt_message(hass, "avail_item2/some/base/topic", "available")
+    await hass.async_block_till_done()
+
     state = hass.states.get("switch.DiscoveryExpansionTest1")
     assert state is not None
     assert state.name == "DiscoveryExpansionTest1"
@@ -474,6 +497,12 @@ async def test_discovery_expansion(hass, mqtt_mock, caplog):
     state = hass.states.get("switch.DiscoveryExpansionTest1")
     assert state.state == STATE_ON
 
+    async_fire_mqtt_message(hass, "some/base/topic/avail_item1", "not_available")
+    await hass.async_block_till_done()
+
+    state = hass.states.get("switch.DiscoveryExpansionTest1")
+    assert state.state == STATE_UNAVAILABLE
+
 
 ABBREVIATIONS_WHITE_LIST = [
     # MQTT client/server/trigger settings