diff --git a/lib/galaxy/model/migrations/alembic/versions_gxy/d619fdfa6168_username_column_unique_constraint.py b/lib/galaxy/model/migrations/alembic/versions_gxy/d619fdfa6168_username_column_unique_constraint.py
new file mode 100644
index 000000000000..22be2d5f5bd7
--- /dev/null
+++ b/lib/galaxy/model/migrations/alembic/versions_gxy/d619fdfa6168_username_column_unique_constraint.py
@@ -0,0 +1,51 @@
+"""Username column unique constraint
+
+Revision ID: d619fdfa6168
+Revises: eee9229a9765
+Create Date: 2024-07-02 13:13:10.325586
+"""
+
+from alembic import op
+
+from galaxy.model.database_object_names import build_index_name
+from galaxy.model.migrations.data_fixes.user_table_fixer import UsernameDeduplicator
+from galaxy.model.migrations.util import (
+    create_index,
+    drop_index,
+    index_exists,
+    transaction,
+)
+
+# revision identifiers, used by Alembic.
+revision = "d619fdfa6168"
+down_revision = "eee9229a9765"
+branch_labels = None
+depends_on = None
+
+table_name = "galaxy_user"
+column_name = "username"
+index_name = build_index_name(table_name, [column_name])
+
+
+def upgrade():
+    with transaction():
+        _fix_duplicate_usernames()
+        # Existing databases may have an existing index we no longer need
+        # New databases will not have that index, so we must check.
+        if index_exists(index_name, table_name, False):
+            drop_index(index_name, table_name)
+        # Create a UNIQUE index
+        create_index(index_name, table_name, [column_name], unique=True)
+
+
+def downgrade():
+    with transaction():
+        drop_index(index_name, table_name)
+        # Restore a non-unique index
+        create_index(index_name, table_name, [column_name])
+
+
+def _fix_duplicate_usernames():
+    """Fix records with duplicate usernames"""
+    connection = op.get_bind()
+    UsernameDeduplicator(connection).run()