diff --git a/src/wp-includes/class-wp-query.php b/src/wp-includes/class-wp-query.php
index 437c82f1dd7f1..59f87613f3251 100644
--- a/src/wp-includes/class-wp-query.php
+++ b/src/wp-includes/class-wp-query.php
@@ -737,6 +737,7 @@ public function fill_query_vars( $query_vars ) {
 	 *                                                   - 'relevance'
 	 *                                                   - 'RAND(x)' (where 'x' is an integer seed value)
 	 *                                                   - 'comment_count'
+	 *                                                   - 'comment_date'
 	 *                                                   - 'meta_value'
 	 *                                                   - 'meta_value_num'
 	 *                                                   - 'post__in'
@@ -1707,6 +1708,7 @@ protected function parse_orderby( $orderby ) {
 			'ID',
 			'menu_order',
 			'comment_count',
+			'comment_date',
 			'rand',
 			'post__in',
 			'post_parent__in',
@@ -1756,6 +1758,9 @@ protected function parse_orderby( $orderby ) {
 			case 'comment_count':
 				$orderby_clause = "{$wpdb->posts}.{$orderby}";
 				break;
+			case 'comment_date':
+				$orderby_clause = 'ISNULL(wp_query_comments_last.comment_date), wp_query_comments_last.comment_date';
+				break;
 			case 'rand':
 				$orderby_clause = 'RAND()';
 				break;
@@ -2488,6 +2493,8 @@ public function get_posts() {
 			$query_vars['order'] = '';
 		}
 
+		$orderby_comment_date = false;
+
 		// Order by.
 		if ( empty( $query_vars['orderby'] ) ) {
 			/*
@@ -2512,6 +2519,10 @@ public function get_posts() {
 						continue;
 					}
 
+					if ( 'comment_date' === $orderby ) {
+						$orderby_comment_date = true;
+					}
+
 					$orderby_array[] = $parsed . ' ' . $this->parse_order( $order );
 				}
 				$orderby = implode( ', ', $orderby_array );
@@ -2527,6 +2538,10 @@ public function get_posts() {
 						continue;
 					}
 
+					if ( 'comment_date' === $orderby ) {
+						$orderby_comment_date = true;
+					}
+
 					$orderby_array[] = $parsed;
 				}
 				$orderby = implode( ' ' . $query_vars['order'] . ', ', $orderby_array );
@@ -2539,6 +2554,16 @@ public function get_posts() {
 			}
 		}
 
+		if ( $orderby_comment_date ) {
+			$join .= " LEFT JOIN (
+				SELECT comment_post_ID, MAX(comment_date) AS comment_date
+				FROM {$wpdb->comments}
+				WHERE comment_approved = '1'
+				AND comment_type != 'note'
+				GROUP BY comment_post_ID
+			) AS wp_query_comments_last ON ( {$wpdb->posts}.ID = wp_query_comments_last.comment_post_ID )";
+		}
+
 		// Order search results by relevance only when another "orderby" is not specified in the query.
 		if ( ! empty( $query_vars['s'] ) ) {
 			$search_orderby = '';
diff --git a/tests/phpunit/tests/query/results.php b/tests/phpunit/tests/query/results.php
index e9ec173d61dfd..8a97db1f0107d 100644
--- a/tests/phpunit/tests/query/results.php
+++ b/tests/phpunit/tests/query/results.php
@@ -633,6 +633,87 @@ public function test_query_orderby_post_parent__in_with_order_desc() {
 		$this->assertSame( $expected_returned_array, wp_list_pluck( $posts, 'post_title' ) );
 	}
 
+	/**
+	 * @ticket 11398
+	 */
+	public function test_query_orderby_comment_date() {
+		$post_ids = self::factory()->post->create_many(
+			4,
+			array(
+				'post_date' => '2020-01-01 00:00:00',
+			)
+		);
+
+		self::factory()->comment->create(
+			array(
+				'comment_post_ID'  => $post_ids[0],
+				'comment_date'     => '2020-01-01 00:00:00',
+				'comment_date_gmt' => '2020-01-04 00:00:00',
+			)
+		);
+		self::factory()->comment->create(
+			array(
+				'comment_post_ID'  => $post_ids[1],
+				'comment_date'     => '2020-01-02 00:00:00',
+				'comment_date_gmt' => '2020-01-02 00:00:00',
+			)
+		);
+		self::factory()->comment->create(
+			array(
+				'comment_post_ID'  => $post_ids[1],
+				'comment_date'     => '2020-01-05 00:00:00',
+				'comment_date_gmt' => '2020-01-05 00:00:00',
+				'comment_approved' => '0',
+			)
+		);
+		self::factory()->comment->create(
+			array(
+				'comment_post_ID'  => $post_ids[2],
+				'comment_date'     => '2019-01-01 00:00:00',
+				'comment_date_gmt' => '2019-01-01 00:00:00',
+			)
+		);
+		self::factory()->comment->create(
+			array(
+				'comment_post_ID'  => $post_ids[2],
+				'comment_date'     => '2020-01-03 00:00:00',
+				'comment_date_gmt' => '2020-01-03 00:00:00',
+			)
+		);
+		self::factory()->comment->create(
+			array(
+				'comment_post_ID'  => $post_ids[3],
+				'comment_date'     => '2020-01-06 00:00:00',
+				'comment_date_gmt' => '2020-01-06 00:00:00',
+				'comment_type'     => 'note',
+			)
+		);
+
+		$query_args = array(
+			'post__in'            => $post_ids,
+			'orderby'             => 'comment_date',
+			'fields'              => 'ids',
+			'posts_per_page'      => -1,
+			'ignore_sticky_posts' => true,
+		);
+
+		$desc_query    = new WP_Query( array_merge( $query_args, array( 'order' => 'DESC' ) ) );
+		$asc_query     = new WP_Query( array_merge( $query_args, array( 'order' => 'ASC' ) ) );
+		$limited_query = new WP_Query(
+			array_merge(
+				$query_args,
+				array(
+					'order'          => 'DESC',
+					'posts_per_page' => 2,
+				)
+			)
+		);
+
+		$this->assertSame( array( $post_ids[2], $post_ids[1], $post_ids[0], $post_ids[3] ), $desc_query->posts );
+		$this->assertSame( array( $post_ids[0], $post_ids[1], $post_ids[2], $post_ids[3] ), $asc_query->posts );
+		$this->assertSame( array( $post_ids[2], $post_ids[1] ), $limited_query->posts );
+	}
+
 	/**
 	 * @ticket 39055
 	 */