diff --git a/src/wp-includes/class-wp-query.php b/src/wp-includes/class-wp-query.php
index 122764d6f9bb2..3082d49a2e9d2 100644
--- a/src/wp-includes/class-wp-query.php
+++ b/src/wp-includes/class-wp-query.php
@@ -1679,6 +1679,7 @@ protected function parse_search_order( &$query_vars ) {
 	 * Converts the given orderby alias (if allowed) to a properly-prefixed value.
 	 *
 	 * @since 4.0.0
+	 * @since 6.9.0 Extends allowed_keys to support ordering by `post_mime_type`.
 	 *
 	 * @global wpdb $wpdb WordPress database abstraction object.
 	 *
@@ -1695,6 +1696,7 @@ protected function parse_orderby( $orderby ) {
 			'post_date',
 			'post_title',
 			'post_modified',
+			'post_mime_type',
 			'post_parent',
 			'post_type',
 			'name',
@@ -1748,6 +1750,7 @@ protected function parse_orderby( $orderby ) {
 			case 'post_author':
 			case 'post_date':
 			case 'post_title':
+			case 'post_mime_type':
 			case 'post_modified':
 			case 'post_parent':
 			case 'post_type':
diff --git a/src/wp-includes/rest-api/endpoints/class-wp-rest-attachments-controller.php b/src/wp-includes/rest-api/endpoints/class-wp-rest-attachments-controller.php
index faeb01c93904a..e25e415a25b66 100644
--- a/src/wp-includes/rest-api/endpoints/class-wp-rest-attachments-controller.php
+++ b/src/wp-includes/rest-api/endpoints/class-wp-rest-attachments-controller.php
@@ -71,6 +71,7 @@ public function register_routes() {
 	 *
 	 * @since 4.7.0
 	 * @since 6.9.0 Extends the `media_type` and `mime_type` request arguments to support array values.
+	 * @since 6.9.0 Extends the `orderby` request argument to support `mime_type`.
 	 *
 	 * @param array           $prepared_args Optional. Array of prepared arguments. Default empty array.
 	 * @param WP_REST_Request $request       Optional. Request to prepare items for.
@@ -112,6 +113,17 @@ protected function prepare_items_query( $prepared_args = array(), $request = nul
 			add_filter( 'wp_allow_query_attachment_by_filename', '__return_true' );
 		}
 
+		// Map to proper WP_Query orderby param.
+		if ( isset( $query_args['orderby'], $request['orderby'] ) ) {
+			$orderby_mappings = array(
+				'mime_type' => 'post_mime_type',
+			);
+
+			if ( isset( $orderby_mappings[ $request['orderby'] ] ) ) {
+				$query_args['orderby'] = $orderby_mappings[ $request['orderby'] ];
+			}
+		}
+
 		return $query_args;
 	}
 
@@ -1355,6 +1367,7 @@ public static function get_filename_from_disposition( $disposition_header ) {
 	 *
 	 * @since 4.7.0
 	 * @since 6.9.0 Extends the `media_type` and `mime_type` request arguments to support array values.
+	 * @since 6.9.0 Extends the `orderby` request argument to support `mime_type`.
 	 *
 	 * @return array Query parameters for the attachment collection as an array.
 	 */
@@ -1383,6 +1396,8 @@ public function get_collection_params() {
 			),
 		);
 
+		$params['orderby']['enum'][] = 'mime_type';
+
 		return $params;
 	}
 
diff --git a/tests/phpunit/tests/query/results.php b/tests/phpunit/tests/query/results.php
index 412d02fe83be6..abd2b7abb13d9 100644
--- a/tests/phpunit/tests/query/results.php
+++ b/tests/phpunit/tests/query/results.php
@@ -20,6 +20,11 @@ class Tests_Query_Results extends WP_UnitTestCase {
 	public static $child_two;
 	public static $child_three;
 	public static $child_four;
+	public static $image1_jpg;
+	public static $image2_jpg;
+	public static $image3_png;
+	public static $audio1_mp3;
+	public static $video1_mp4;
 
 	public static function wpSetUpBeforeClass( WP_UnitTest_Factory $factory ) {
 		$cat_a           = $factory->term->create(
@@ -292,6 +297,47 @@ public static function wpSetUpBeforeClass( WP_UnitTest_Factory $factory ) {
 			)
 		);
 		self::$post_ids[]   = self::$child_four;
+
+		self::$image1_jpg = $factory->attachment->create_object(
+			'image1.jpg',
+			0,
+			array(
+				'post_mime_type' => 'image/jpeg',
+				'post_date'      => '2025-09-29 06:22:49',
+			)
+		);
+		self::$image2_jpg = $factory->attachment->create_object(
+			'image2.jpg',
+			0,
+			array(
+				'post_mime_type' => 'image/jpeg',
+				'post_date'      => '2025-09-29 06:22:49',
+			)
+		);
+		self::$image3_png = $factory->attachment->create_object(
+			'image3.png',
+			0,
+			array(
+				'post_mime_type' => 'image/png',
+				'post_date'      => '2025-09-29 06:22:49',
+			)
+		);
+		self::$audio1_mp3 = $factory->attachment->create_object(
+			'audio1.mp3',
+			0,
+			array(
+				'post_mime_type' => 'audio/mpeg',
+				'post_date'      => '2025-09-29 06:22:49',
+			)
+		);
+		self::$video1_mp4 = $factory->attachment->create_object(
+			'video1.mp4',
+			0,
+			array(
+				'post_mime_type' => 'video/mp4',
+				'post_date'      => '2025-09-29 06:22:49',
+			)
+		);
 	}
 
 	public function set_up() {
@@ -1264,4 +1310,53 @@ public function test_main_comments_feed_includes_attachment_comments() {
 		$feed_comment = $this->q->next_comment();
 		$this->assertEquals( $comment_id, $feed_comment->comment_ID );
 	}
+
+	/**
+	 * @ticket 64073
+	 */
+	public function test_attachment_orderby_post_mime_type() {
+		$all_attachments_desc = $this->q->query(
+			array(
+				'post_type'   => 'attachment',
+				'orderby'     => 'post_mime_type',
+				'post_status' => 'inherit',
+				'order'       => 'desc',
+			)
+		);
+
+		$this->assertCount( 5, $all_attachments_desc );
+
+		$this->assertSame(
+			array(
+				self::$video1_mp4,
+				self::$image3_png,
+				self::$image1_jpg,
+				self::$image2_jpg,
+				self::$audio1_mp3,
+			),
+			wp_list_pluck( $all_attachments_desc, 'ID' ),
+			'Order by post_mime_type order desc returns incorrect order'
+		);
+
+		$all_attachments_asc = $this->q->query(
+			array(
+				'post_type'   => 'attachment',
+				'orderby'     => 'post_mime_type',
+				'post_status' => 'inherit',
+				'order'       => 'asc',
+			)
+		);
+
+		$this->assertSame(
+			array(
+				self::$audio1_mp3,
+				self::$image1_jpg,
+				self::$image2_jpg,
+				self::$image3_png,
+				self::$video1_mp4,
+			),
+			wp_list_pluck( $all_attachments_asc, 'ID' ),
+			'Order by post_mime_type order asc returns incorrect order'
+		);
+	}
 }
diff --git a/tests/phpunit/tests/rest-api/rest-attachments-controller.php b/tests/phpunit/tests/rest-api/rest-attachments-controller.php
index bc1ca41b578ee..f8c32c85d4b15 100644
--- a/tests/phpunit/tests/rest-api/rest-attachments-controller.php
+++ b/tests/phpunit/tests/rest-api/rest-attachments-controller.php
@@ -3097,4 +3097,69 @@ public function test_edit_image_vertical_flip_only() {
 		// The controller converts the integer values to booleans: 0 !== (int) 1 = true.
 		$this->assertSame( array( true, false ), WP_Image_Editor_Mock::$spy['flip'][0], 'Vertical flip of the image is not identical.' );
 	}
+
+	/**
+	 * Test that the `orderby` parameter works with the `mime_type` parameter.
+	 *
+	 * @ticket 64073
+	 */
+	public function test_get_items_orderby_mime_type() {
+		$jpeg_id = self::factory()->attachment->create_object(
+			self::$test_file,
+			0,
+			array(
+				'post_mime_type' => 'image/jpeg',
+				'post_excerpt'   => 'A sample caption',
+			)
+		);
+
+		$png_id = self::factory()->attachment->create_object(
+			self::$test_file2,
+			0,
+			array(
+				'post_mime_type' => 'image/png',
+				'post_excerpt'   => 'A sample caption',
+			)
+		);
+
+		$avif_id = self::factory()->attachment->create_object(
+			self::$test_avif_file,
+			0,
+			array(
+				'post_mime_type' => 'video/avif',
+				'post_excerpt'   => 'A sample caption',
+			)
+		);
+
+		$svg_id = self::factory()->attachment->create_object(
+			self::$test_svg_file,
+			0,
+			array(
+				'post_mime_type' => 'image/svg+xml',
+				'post_excerpt'   => 'A sample caption',
+			)
+		);
+
+		$request = new WP_REST_Request( 'GET', '/wp/v2/media' );
+		$request->set_param( '_fields', 'id,mime_type' );
+
+		// Check ordering. Default ORDER is DESC.
+		$request->set_param( 'orderby', 'mime_type' );
+		$response = rest_get_server()->dispatch( $request );
+		$data     = $response->get_data();
+		$this->assertCount( 4, $data, 'Response count for orderby DESC mime_type is not 4' );
+		// Check that ordering is working by verifying the mime types are in order
+		$mime_types    = array_column( $data, 'mime_type' );
+		$expected_desc = array( 'video/avif', 'image/svg+xml', 'image/png', 'image/jpeg' );
+		$this->assertSame( $expected_desc, $mime_types, 'MIME types not in expected DESC order' );
+
+		// ASC order.
+		$request->set_param( 'order', 'asc' );
+		$response = rest_get_server()->dispatch( $request );
+		$data     = $response->get_data();
+
+		$mime_types   = array_column( $data, 'mime_type' );
+		$expected_asc = array( 'image/jpeg', 'image/png', 'image/svg+xml', 'video/avif' );
+		$this->assertSame( $expected_asc, $mime_types, 'MIME types not in expected ASC order' );
+	}
 }
diff --git a/tests/qunit/fixtures/wp-api-generated.js b/tests/qunit/fixtures/wp-api-generated.js
index bc9ea0a2dc424..fceb635aca10c 100644
--- a/tests/qunit/fixtures/wp-api-generated.js
+++ b/tests/qunit/fixtures/wp-api-generated.js
@@ -2903,7 +2903,8 @@ mockedApiResponse.Schema = {
                                 "relevance",
                                 "slug",
                                 "include_slugs",
-                                "title"
+                                "title",
+                                "mime_type"
                             ],
                             "required": false
                         },