diff --git a/auto_submit/lib/service/pull_request_validation_service.dart b/auto_submit/lib/service/pull_request_validation_service.dart
index 7a3f0dd..322c352 100644
--- a/auto_submit/lib/service/pull_request_validation_service.dart
+++ b/auto_submit/lib/service/pull_request_validation_service.dart
@@ -59,11 +59,14 @@
     final github.RepositorySlug slug = messagePullRequest.base!.repo!.slug();
     final int prNumber = messagePullRequest.number!;
 
+    // If a pull request is currently in the merge queue do not touch it. Let
+    // the merge queue merge it, or kick it out of the merge queue.
     if (messagePullRequest.isMergeQueueEnabled) {
       if (result.repository!.pullRequest!.isInMergeQueue) {
         log.info(
           '${slug.fullName}/$prNumber is already in the merge queue. Skipping.',
         );
+        await pubsub.acknowledge(config.pubsubRevertRequestSubscription, ackId);
         return;
       }
     }
@@ -140,7 +143,7 @@
       await githubService.createComment(slug, prNumber, message);
       log.info(message);
     } else {
-      log.info('Pull Request ${slug.fullName}/$prNumber was merged successfully!');
+      log.info('Pull Request ${slug.fullName}/$prNumber was ${processed.method.pastTenseLabel} successfully!');
       log.info('Attempting to insert a pull request record into the database for $prNumber');
       await insertPullRequestRecord(
         config: config,
diff --git a/auto_submit/lib/service/revert_request_validation_service.dart b/auto_submit/lib/service/revert_request_validation_service.dart
index 125d69e..83d17a4 100644
--- a/auto_submit/lib/service/revert_request_validation_service.dart
+++ b/auto_submit/lib/service/revert_request_validation_service.dart
@@ -218,6 +218,18 @@
     final GithubService githubService = await config.createGithubService(slug);
     final int prNumber = messagePullRequest.number!;
 
+    // If a pull request is currently in the merge queue do not touch it. Let
+    // the merge queue merge it, or kick it out of the merge queue.
+    if (messagePullRequest.isMergeQueueEnabled) {
+      if (result.repository!.pullRequest!.isInMergeQueue) {
+        log.info(
+          '${slug.fullName}/$prNumber is already in the merge queue. Skipping.',
+        );
+        await pubsub.acknowledge(config.pubsubRevertRequestSubscription, ackId);
+        return;
+      }
+    }
+
     // Check to make sure the repository allows review-less revert pull requests
     // so that we can reassign if needed otherwise autoapprove the pull request.
     final RepositoryConfiguration repositoryConfiguration = await config.getRepositoryConfiguration(slug);
@@ -304,7 +316,7 @@
       final Message discordMessage = craftDiscordRevertMessage(messagePullRequest);
       discordNotification.notifyDiscordChannelWebhook(jsonEncode(discordMessage.toJson()));
 
-      log.info('Pull Request ${slug.fullName}/$prNumber was merged successfully!');
+      log.info('Pull Request ${slug.fullName}/$prNumber was ${processed.method.pastTenseLabel} successfully!');
       log.info('Attempting to insert a pull request record into the database for $prNumber');
       await insertPullRequestRecord(
         config: config,
diff --git a/auto_submit/lib/service/validation_service.dart b/auto_submit/lib/service/validation_service.dart
index 9f1adfd..9e29565 100644
--- a/auto_submit/lib/service/validation_service.dart
+++ b/auto_submit/lib/service/validation_service.dart
@@ -101,10 +101,10 @@
     } catch (e) {
       final message = 'Failed to enqueue ${slug.fullName}/${restPullRequest.number} with $e';
       log.severe(message);
-      return (result: false, message: message);
+      return (result: false, message: message, method: SubmitMethod.enqueue);
     }
 
-    return (result: true, message: restPullRequest.title!);
+    return (result: true, message: restPullRequest.title!, method: SubmitMethod.enqueue);
   }
 
   Future<MergeResult> _mergePullRequest(int number, String commitMessage, github.RepositorySlug slug) async {
@@ -129,16 +129,16 @@
       if (result != null && !merged) {
         final String message = 'Failed to merge ${slug.fullName}/$number with ${result?.message}';
         log.severe(message);
-        return (result: false, message: message);
+        return (result: false, message: message, method: SubmitMethod.merge);
       }
     } catch (e) {
       // Catch graphql client init exceptions.
       final String message = 'Failed to merge ${slug.fullName}/$number with $e';
       log.severe(message);
-      return (result: false, message: message);
+      return (result: false, message: message, method: SubmitMethod.merge);
     }
 
-    return (result: true, message: commitMessage);
+    return (result: true, message: commitMessage, method: SubmitMethod.merge);
   }
 
   /// Insert a merged pull request record into the database.
@@ -183,9 +183,28 @@
   }
 }
 
+/// Method used to submit the PR for merging.
+enum SubmitMethod {
+  /// The PR is enqueued into the merge queue, and the merge queue is responsible
+  /// for merging the PR.
+  enqueue('enqueued'),
+
+  /// The PR is immediately merged into the target branch.
+  ///
+  /// This is the old method for merging PRs, used by repos where merge queues
+  /// are not (yet?) enabled.
+  merge('merged');
+
+  const SubmitMethod(this.pastTenseLabel);
+
+  /// The verb in past tense used to describe what happened to a PR when this
+  /// submit method was used, e.g. "merged".
+  final String pastTenseLabel;
+}
+
 /// Small wrapper class to allow us to capture and create a comment in the PR with
 /// the issue that caused the merge failure.
-typedef MergeResult = ({bool result, String message});
+typedef MergeResult = ({bool result, String message, SubmitMethod method});
 
 /// Function signature that will be executed with retries.
 typedef RetryHandler = Function();
diff --git a/auto_submit/test/service/pull_request_validation_service_test.dart b/auto_submit/test/service/pull_request_validation_service_test.dart
index 7e740bc..4124c67 100644
--- a/auto_submit/test/service/pull_request_validation_service_test.dart
+++ b/auto_submit/test/service/pull_request_validation_service_test.dart
@@ -645,6 +645,7 @@
         mergeable: true,
       );
 
+      unawaited(pubsub.publish(config.pubsubRevertRequestSubscription, pullRequest));
       await validationService.processPullRequest(
         config: config,
         result: createQueryResult(flutterRequest),
@@ -658,6 +659,7 @@
         logs,
         contains('[INFO] auto_submit: flutter/flaux/0 is already in the merge queue. Skipping.'),
       );
+      assert(pubsub.messagesQueue.isEmpty);
     });
   });
 }
diff --git a/auto_submit/test/service/revert_request_validation_service_test.dart b/auto_submit/test/service/revert_request_validation_service_test.dart
index 87a3fe7..622cd16 100644
--- a/auto_submit/test/service/revert_request_validation_service_test.dart
+++ b/auto_submit/test/service/revert_request_validation_service_test.dart
@@ -9,6 +9,7 @@
 import 'package:auto_submit/model/auto_submit_query_result.dart' as auto hide PullRequest;
 import 'package:auto_submit/requests/github_pull_request_event.dart';
 import 'package:auto_submit/model/discord_message.dart';
+import 'package:auto_submit/service/log.dart';
 import 'package:auto_submit/service/revert_request_validation_service.dart';
 import 'package:auto_submit/service/validation_service.dart';
 import 'package:auto_submit/validations/validation.dart';
@@ -1233,6 +1234,59 @@
       expect(githubService.labelRemoved, true);
       assert(pubsub.messagesQueue.isEmpty);
     });
+
+    test('Do not re-enqueue already enqueued pull requests', () async {
+      // Use a test slug that has MQ enabled
+      slug = RepositorySlug('flutter', 'flaux');
+
+      final logs = <String>[];
+      final logSub = log.onRecord.listen((record) {
+        logs.add(record.toString());
+      });
+
+      final FakePubSub pubsub = FakePubSub();
+
+      final PullRequestHelper flutterRequest = PullRequestHelper(
+        prNumber: 0,
+        lastCommitHash: oid,
+        reviews: <PullRequestReviewHelper>[],
+        isInMergeQueue: true,
+      );
+
+      final auto.QueryResult queryResult = createQueryResult(flutterRequest);
+
+      final PullRequest pullRequest = generatePullRequest(
+        prNumber: 0,
+        repoName: slug.name,
+        labelName: 'revert of',
+        body: sampleRevertBody.replaceAll('\n', ''),
+      );
+
+      final GithubPullRequestEvent githubPullRequestEvent = GithubPullRequestEvent(
+        pullRequest: pullRequest,
+        action: 'labeled',
+        sender: User(login: 'auto-submit[bot]'),
+      );
+
+      // Process the pull request
+      unawaited(pubsub.publish(config.pubsubRevertRequestSubscription, pullRequest));
+      await validationService.processRevertOfRequest(
+        result: queryResult,
+        githubPullRequestEvent: githubPullRequestEvent,
+        ackId: 'test',
+        pubsub: pubsub,
+      );
+      await logSub.cancel();
+
+      // Expectations
+      expect(
+        logs,
+        contains('[INFO] auto_submit: flutter/flaux/0 is already in the merge queue. Skipping.'),
+      );
+      expect(githubService.issueComment, isNull);
+      expect(githubService.labelRemoved, false);
+      assert(pubsub.messagesQueue.isEmpty);
+    });
   });
 
   group('Craft discord message', () {