diff --git a/homeassistant/components/smartthings/sensor.py b/homeassistant/components/smartthings/sensor.py
index 2164e432edcd7cc16a8f06d3240e2718d053033c..5a2fdcf3854b6d21e99f848f3c8be1e28d38d7fa 100644
--- a/homeassistant/components/smartthings/sensor.py
+++ b/homeassistant/components/smartthings/sensor.py
@@ -561,6 +561,8 @@ CAPABILITY_TO_SENSORS: dict[
             SmartThingsSensorEntityDescription(
                 key=Attribute.COMPLETION_TIME,
                 translation_key="completion_time",
+                device_class=SensorDeviceClass.TIMESTAMP,
+                value_fn=dt_util.parse_datetime,
             )
         ],
     },
diff --git a/tests/components/smartthings/snapshots/test_sensor.ambr b/tests/components/smartthings/snapshots/test_sensor.ambr
index 5909fec2707f61ef83dc4ce471c9f73854f82098..b939547ca32c656241acfc925441ad37780d811a 100644
--- a/tests/components/smartthings/snapshots/test_sensor.ambr
+++ b/tests/components/smartthings/snapshots/test_sensor.ambr
@@ -1710,7 +1710,7 @@
     'name': None,
     'options': dict({
     }),
-    'original_device_class': None,
+    'original_device_class': <SensorDeviceClass.TIMESTAMP: 'timestamp'>,
     'original_icon': None,
     'original_name': 'Completion time',
     'platform': 'smartthings',
@@ -1724,6 +1724,7 @@
 # name: test_all_entities[da_ks_microwave_0101x][sensor.microwave_completion_time-state]
   StateSnapshot({
     'attributes': ReadOnlyDict({
+      'device_class': 'timestamp',
       'friendly_name': 'Microwave Completion time',
     }),
     'context': <ANY>,
@@ -1731,7 +1732,7 @@
     'last_changed': <ANY>,
     'last_reported': <ANY>,
     'last_updated': <ANY>,
-    'state': '2025-02-08T21:13:36.184Z',
+    'state': '2025-02-08T21:13:36+00:00',
   })
 # ---
 # name: test_all_entities[da_ks_microwave_0101x][sensor.microwave_job_state-entry]