diff --git a/src/applications/project/query/PhabricatorProjectQuery.php b/src/applications/project/query/PhabricatorProjectQuery.php
--- a/src/applications/project/query/PhabricatorProjectQuery.php
+++ b/src/applications/project/query/PhabricatorProjectQuery.php
@@ -6,6 +6,7 @@
   private $ids;
   private $phids;
   private $memberPHIDs;
+  private $watcherPHIDs;
   private $slugs;
   private $slugNormals;
   private $slugMap;
@@ -62,6 +63,11 @@
     return $this;
   }
 
+  public function withWatcherPHIDs(array $watcher_phids) {
+    $this->watcherPHIDs = $watcher_phids;
+    return $this;
+  }
+
   public function withSlugs(array $slugs) {
     $this->slugs = $slugs;
     return $this;
@@ -436,6 +442,13 @@
         $this->memberPHIDs);
     }
 
+    if ($this->watcherPHIDs !== null) {
+      $where[] = qsprintf(
+        $conn,
+        'w.dst IN (%Ls)',
+        $this->watcherPHIDs);
+    }
+
     if ($this->slugs !== null) {
       $where[] = qsprintf(
         $conn,
@@ -549,7 +562,7 @@
   }
 
   protected function shouldGroupQueryResultRows() {
-    if ($this->memberPHIDs || $this->nameTokens) {
+    if ($this->memberPHIDs || $this->watcherPHIDs || $this->nameTokens) {
       return true;
     }
     return parent::shouldGroupQueryResultRows();
@@ -566,6 +579,14 @@
         PhabricatorProjectMaterializedMemberEdgeType::EDGECONST);
     }
 
+    if ($this->watcherPHIDs !== null) {
+      $joins[] = qsprintf(
+        $conn,
+        'JOIN %T w ON w.src = p.phid AND w.type = %d',
+        PhabricatorEdgeConfig::TABLE_NAME_EDGE,
+        PhabricatorObjectHasWatcherEdgeType::EDGECONST);
+    }
+
     if ($this->slugs !== null) {
       $joins[] = qsprintf(
         $conn,
diff --git a/src/applications/project/query/PhabricatorProjectSearchEngine.php b/src/applications/project/query/PhabricatorProjectSearchEngine.php
--- a/src/applications/project/query/PhabricatorProjectSearchEngine.php
+++ b/src/applications/project/query/PhabricatorProjectSearchEngine.php
@@ -26,6 +26,10 @@
         ->setLabel(pht('Members'))
         ->setKey('memberPHIDs')
         ->setAliases(array('member', 'members')),
+      id(new PhabricatorUsersSearchField())
+        ->setLabel(pht('Watchers'))
+        ->setKey('watcherPHIDs')
+        ->setAliases(array('watcher', 'watchers')),
       id(new PhabricatorSearchSelectField())
         ->setLabel(pht('Status'))
         ->setKey('status')
@@ -54,6 +58,10 @@
       $query->withMemberPHIDs($map['memberPHIDs']);
     }
 
+    if ($map['watcherPHIDs']) {
+      $query->withWatcherPHIDs($map['watcherPHIDs']);
+    }
+
     if ($map['status']) {
       $status = idx($this->getStatusValues(), $map['status']);
       if ($status) {