diff --git a/src/repository/api/ArcanistGitAPI.php b/src/repository/api/ArcanistGitAPI.php
--- a/src/repository/api/ArcanistGitAPI.php
+++ b/src/repository/api/ArcanistGitAPI.php
@@ -1213,4 +1213,12 @@
     $this->resolvedHeadCommit = null;
   }
 
+  public function setSingleCommit($symbolic_commit) {
+    list($parent) = $this->execxLocal(
+      'rev-list %s --skip=1 --max-count=1', $symbolic_commit);
+    $parent = rtrim($parent, "\n");
+    $this->setBaseCommit($parent);
+    $this->setHeadCommit($symbolic_commit);
+  }
+
 }
diff --git a/src/workflow/ArcanistDiffWorkflow.php b/src/workflow/ArcanistDiffWorkflow.php
--- a/src/workflow/ArcanistDiffWorkflow.php
+++ b/src/workflow/ArcanistDiffWorkflow.php
@@ -182,6 +182,15 @@
           'never-apply-patches' => '--nolint suppresses lint.',
         ),
       ),
+      'commit' => array(
+        'param' => 'revision_id',
+        'help' => 'Single commit to generate diff from.',
+        'conflicts' => array(
+          '--base' => '--commit suppresses --base.',
+          '--head' => '--commit suppresses --head.'
+        ),
+        'supports' => array('git'),
+      ),
       'only' => array(
         'help' =>
           'Only generate a diff, without running lint, unit tests, or other '.
@@ -450,6 +459,10 @@
       }
 
       $repo = $this->getRepositoryAPI();
+      if ($this->getArgument('commit')) {
+        $repo->setSingleCommit($this->getArgument('commit'));
+      }
+
       $head_commit = $this->getArgument('head');
       if ($head_commit !== null) {
         $repo->setHeadCommit($head_commit);