diff --git a/docs/changelog/122731.yaml b/docs/changelog/122731.yaml
new file mode 100644
index 0000000000000..afde587a9538b
--- /dev/null
+++ b/docs/changelog/122731.yaml
@@ -0,0 +1,5 @@
+pr: 122731
+summary: Fork post-snapshot-delete cleanup off master thread
+area: Snapshot/Restore
+type: bug
+issues: []
diff --git a/rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/snapshot.delete/10_basic.yml b/rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/snapshot.delete/10_basic.yml
index 5a60f76f6da2c..84e0d5b3e524a 100644
--- a/rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/snapshot.delete/10_basic.yml
+++ b/rest-api-spec/src/yamlRestTest/resources/rest-api-spec/test/snapshot.delete/10_basic.yml
@@ -68,3 +68,10 @@ setup:
         wait_for_completion: false
 
   - match: { acknowledged: true }
+
+  # now create another snapshot just to ensure that the async delete finishes before the test cleanup runs:
+  - do:
+      snapshot.create:
+        repository: test_repo_create_1
+        snapshot: barrier_snapshot
+        wait_for_completion: true
diff --git a/server/src/internalClusterTest/java/org/elasticsearch/snapshots/RepositoriesIT.java b/server/src/internalClusterTest/java/org/elasticsearch/snapshots/RepositoriesIT.java
index c318ebf78dd96..562f752b82220 100644
--- a/server/src/internalClusterTest/java/org/elasticsearch/snapshots/RepositoriesIT.java
+++ b/server/src/internalClusterTest/java/org/elasticsearch/snapshots/RepositoriesIT.java
@@ -508,6 +508,12 @@ public void taskSucceeded(ClusterStateTaskListener clusterStateTaskListener, Obj
             .orElseThrow()
             .queue();
 
+        // There is one task in the queue for computing and forking the cleanup work.
+        assertThat(queueLength.getAsInt(), equalTo(1));
+
+        safeAwait(barrier); // unblock the barrier thread and let it process the queue
+        safeAwait(barrier); // wait for the queue to be processed
+
         // There are indexCount (=3*snapshotPoolSize) index-deletion tasks, plus one for cleaning up the root metadata. However, the
         // throttled runner only enqueues one task per SNAPSHOT thread to start with, and then the eager runner adds another one. This shows
         // we are not spamming the threadpool with all the tasks at once, which means that other snapshot activities can run alongside this
diff --git a/server/src/main/java/org/elasticsearch/repositories/RepositoryData.java b/server/src/main/java/org/elasticsearch/repositories/RepositoryData.java
index 2c429954f5f49..e89998dc919e6 100644
--- a/server/src/main/java/org/elasticsearch/repositories/RepositoryData.java
+++ b/server/src/main/java/org/elasticsearch/repositories/RepositoryData.java
@@ -29,6 +29,7 @@
 import org.elasticsearch.snapshots.SnapshotInfo;
 import org.elasticsearch.snapshots.SnapshotState;
 import org.elasticsearch.snapshots.SnapshotsService;
+import org.elasticsearch.threadpool.ThreadPool;
 import org.elasticsearch.xcontent.XContentBuilder;
 import org.elasticsearch.xcontent.XContentParser;
 
@@ -377,6 +378,7 @@ private static boolean isIndexToUpdateAfterRemovingSnapshots(
      * @return map of index to index metadata blob id to delete
      */
     public Map<IndexId, Collection<String>> indexMetaDataToRemoveAfterRemovingSnapshots(Collection<SnapshotId> snapshotIds) {
+        assert ThreadPool.assertCurrentThreadPool(ThreadPool.Names.SNAPSHOT);
         Iterator<IndexId> indicesForSnapshot = indicesToUpdateAfterRemovingSnapshot(snapshotIds);
         final Set<String> allRemainingIdentifiers = indexMetaDataGenerations.lookup.entrySet()
             .stream()
diff --git a/server/src/main/java/org/elasticsearch/repositories/blobstore/BlobStoreRepository.java b/server/src/main/java/org/elasticsearch/repositories/blobstore/BlobStoreRepository.java
index 11386eba10196..e3ea37c6a4b20 100644
--- a/server/src/main/java/org/elasticsearch/repositories/blobstore/BlobStoreRepository.java
+++ b/server/src/main/java/org/elasticsearch/repositories/blobstore/BlobStoreRepository.java
@@ -1134,14 +1134,20 @@ private void runWithUniqueShardMetadataNaming(ActionListener<RepositoryData> rep
                     );
                 })
 
-                .<RepositoryData>andThen((l, newRepositoryData) -> {
-                    l.onResponse(newRepositoryData);
-                    // Once we have updated the repository, run the unreferenced blobs cleanup in parallel to shard-level snapshot deletion
-                    try (var refs = new RefCountingRunnable(onCompletion)) {
-                        cleanupUnlinkedRootAndIndicesBlobs(newRepositoryData, refs.acquireListener());
-                        cleanupUnlinkedShardLevelBlobs(refs.acquireListener());
+                .<RepositoryData>andThen(
+                    // writeIndexGen finishes on master-service thread so must fork here.
+                    snapshotExecutor,
+                    threadPool.getThreadContext(),
+                    (l, newRepositoryData) -> {
+                        l.onResponse(newRepositoryData);
+                        // Once we have updated the repository, run the unreferenced blobs cleanup in parallel to shard-level snapshot
+                        // deletion
+                        try (var refs = new RefCountingRunnable(onCompletion)) {
+                            cleanupUnlinkedRootAndIndicesBlobs(newRepositoryData, refs.acquireListener());
+                            cleanupUnlinkedShardLevelBlobs(refs.acquireListener());
+                        }
                     }
-                })
+                )
 
                 .addListener(repositoryDataUpdateListener);
         }