diff --git a/src/lando/api/legacy/workers/landing_worker.py b/src/lando/api/legacy/workers/landing_worker.py
index 26b3abae3..e4084a689 100644
--- a/src/lando/api/legacy/workers/landing_worker.py
+++ b/src/lando/api/legacy/workers/landing_worker.py
@@ -50,6 +50,7 @@
 )
 from lando.pushlog.pushlog import PushLog, PushLogForRepo
 from lando.utils.config import read_lando_config
+from lando.utils.github import GitHubAPIClient
 from lando.utils.tasks import phab_trigger_repo_update
 
 logger = logging.getLogger(__name__)
@@ -144,6 +145,15 @@ def run_job(self, job: LandingJob) -> bool:
         job.set_landed_commit_ids()
         job.transition_status(JobAction.LAND, commit_id=commit_id)
 
+        if job.is_pull_request_job:
+            # TODO: move this to different method, and retry if needed.
+            # NOTE: This may need to happen on the revision-level when stack support is added.
+            pull_number = job.revisions.first().pull_number
+            message = f"Pull request closed by commit {commit_id}"
+            client = GitHubAPIClient(job.target_repo)
+            client.add_comment_to_pull_request(pull_number, message)
+            client.close_pull_request(pull_number)
+
         mots_path = Path(repo.path) / "mots.yaml"
         if mots_path.exists():
             logger.info(f"{mots_path} found, setting reviewer data.")
diff --git a/src/lando/main/models/landing_job.py b/src/lando/main/models/landing_job.py
index 4b28b4428..2ae4be170 100644
--- a/src/lando/main/models/landing_job.py
+++ b/src/lando/main/models/landing_job.py
@@ -47,6 +47,11 @@ class LandingJob(BaseJob):
         Revision, through="RevisionLandingJob", related_name="landing_jobs"
     )
 
+    @property
+    def is_pull_request_job(self) -> bool:
+        """Return True if all revisions in the landing job have a pull_number set."""
+        return not self.revisions.filter(pull_number__isnull=True).exists()
+
     @property
     def landed_phabricator_revisions(self) -> dict:
         """Return a mapping associating Phabricator revision IDs with the ID of the landed Diff."""