diff --git a/google/cloud/pubsub_v1/publisher/_batch/thread.py b/google/cloud/pubsub_v1/publisher/_batch/thread.py
index 36dd3b946..3f9a17f74 100644
--- a/google/cloud/pubsub_v1/publisher/_batch/thread.py
+++ b/google/cloud/pubsub_v1/publisher/_batch/thread.py
@@ -207,9 +207,11 @@ def commit(self):
 
     def _start_commit_thread(self):
         """Start a new thread to actually handle the commit."""
-
+        # NOTE: If the thread is *not* a daemon, a memory leak exists due to a CPython issue.
+        # https://github.com/googleapis/python-pubsub/issues/395#issuecomment-829910303
+        # https://github.com/googleapis/python-pubsub/issues/395#issuecomment-830092418
         commit_thread = threading.Thread(
-            name="Thread-CommitBatchPublisher", target=self._commit
+            name="Thread-CommitBatchPublisher", target=self._commit, daemon=True
         )
         commit_thread.start()
 
diff --git a/google/cloud/pubsub_v1/publisher/client.py b/google/cloud/pubsub_v1/publisher/client.py
index 7e6801de0..4703cc3c4 100644
--- a/google/cloud/pubsub_v1/publisher/client.py
+++ b/google/cloud/pubsub_v1/publisher/client.py
@@ -375,8 +375,13 @@ def _ensure_commit_timer_runs_no_lock(self):
 
     def _start_commit_thread(self):
         """Start a new thread to actually wait and commit the sequencers."""
+        # NOTE: If the thread is *not* a daemon, a memory leak exists due to a CPython issue.
+        # https://github.com/googleapis/python-pubsub/issues/395#issuecomment-829910303
+        # https://github.com/googleapis/python-pubsub/issues/395#issuecomment-830092418
         self._commit_thread = threading.Thread(
-            name="Thread-PubSubBatchCommitter", target=self._wait_and_commit_sequencers
+            name="Thread-PubSubBatchCommitter",
+            target=self._wait_and_commit_sequencers,
+            daemon=True,
         )
         self._commit_thread.start()