diff --git a/lib/block-supports/index.php b/lib/block-supports/index.php
index 4d91d6f9cc77e5..d363999b099078 100644
--- a/lib/block-supports/index.php
+++ b/lib/block-supports/index.php
@@ -35,6 +35,8 @@ function gutenberg_apply_block_supports( $block_content, $block ) {
 		return $block_content;
 	}
 
+	$block = gutenberg_apply_default_block_attribute_values( $block );
+
 	$block_type = WP_Block_Type_Registry::get_instance()->get_registered( $block['blockName'] );
 	// If no render_callback, assume styles have been previously handled.
 	if ( ! $block_type || ! $block_type->render_callback ) {
@@ -106,3 +108,25 @@ function gutenberg_apply_block_supports( $block_content, $block ) {
 function gutenberg_normalize_css_rule( $css_rule_string ) {
 	return trim( implode( ': ', preg_split( '/\s*:\s*/', $css_rule_string, 2 ) ), ';' );
 }
+
+/**
+ * Applies default values to block attributes if no values are set.
+ *
+ * @param  object $block The block to apply default values to.
+ * @return object The block with default values applied to its attributes.
+ */
+function gutenberg_apply_default_block_attribute_values( $block ) {
+	$block_type = WP_Block_Type_Registry::get_instance()->get_registered( $block['blockName'] );
+	// If no render_callback, assume default values have been previously handled.
+	if ( ! $block_type || ! $block_type->render_callback || ! $block_type->attributes ) {
+		return $block;
+	}
+
+	foreach ( $block_type->attributes as $attribute_name => $attribute_value ) {
+		if ( ! isset( $block['attrs'][ $attribute_name ] ) && isset( $attribute_value['default'] ) ) {
+			$block['attrs'][ $attribute_name ] = $attribute_value['default'];
+		}
+	}
+
+	return $block;
+}
diff --git a/phpunit/class-block-supported-styles-test.php b/phpunit/class-block-supported-styles-test.php
index 9e6e3cba767ef4..ca06c0563ff19d 100644
--- a/phpunit/class-block-supported-styles-test.php
+++ b/phpunit/class-block-supported-styles-test.php
@@ -606,6 +606,53 @@ function test_all_supported() {
 		$this->assert_content_and_styles_and_classes_match( $block, $expected_classes, $expected_styles );
 	}
 
+	/**
+	 * Tests that default values are applied if none are saved.
+	 */
+	function test_default_values_applied() {
+		$block_type_settings = array(
+			'attributes'      => array(
+				'textColor'       => array( 'default' => 'red' ),
+				'backgroundColor' => array( 'default' => 'black' ),
+				'style'           => array(
+					'default' => array(
+						'color'      => array(
+							'link' => 'var:preset|color|red',
+						),
+						'typography' => array(
+							'fontSize'   => '10',
+							'lineHeight' => '10',
+						),
+					),
+				),
+			),
+			'supports'        => array(
+				'__experimentalColor'      => array(
+					'gradients' => true,
+					'linkColor' => true,
+				),
+				'__experimentalFontSize'   => true,
+				'__experimentalLineHeight' => true,
+				'align'                    => true,
+			),
+			'render_callback' => true,
+		);
+		$this->register_block_type( 'core/example', $block_type_settings );
+
+		$block = array(
+			'blockName'    => 'core/example',
+			'attrs'        => array(),
+			'innerBlock'   => array(),
+			'innerContent' => array(),
+			'innerHTML'    => array(),
+		);
+
+		$expected_classes = 'foo-bar-class wp-block-example has-text-color has-red-color has-link-color has-background has-black-background-color';
+		$expected_styles  = 'test: style; --wp--style--color--link: var(--wp--preset--color--red); font-size: 10px; line-height: 10;';
+
+		$this->assert_content_and_styles_and_classes_match( $block, $expected_classes, $expected_styles );
+	}
+
 	/**
 	 * Tests that only styles for the supported flag are added.
 	 * Verify one support enabled does not imply multiple supports enabled.