diff --git a/backport-changelog/7.1/11245.md b/backport-changelog/7.1/11245.md
new file mode 100644
index 00000000000000..7324c0d65f4cc4
--- /dev/null
+++ b/backport-changelog/7.1/11245.md
@@ -0,0 +1,3 @@
+https://github.com/WordPress/wordpress-develop/pull/11245
+
+* https://github.com/WordPress/gutenberg/pull/76079
diff --git a/lib/compat/wordpress-7.1/class-gutenberg-icons-registry-7-1.php b/lib/compat/wordpress-7.1/class-gutenberg-icons-registry-7-1.php
index e827056064e7b1..727064c9b9e7a0 100644
--- a/lib/compat/wordpress-7.1/class-gutenberg-icons-registry-7-1.php
+++ b/lib/compat/wordpress-7.1/class-gutenberg-icons-registry-7-1.php
@@ -50,6 +50,127 @@ protected function __construct() {
 		}
 	}
 
+	/**
+	 * Registers an icon.
+	 *
+	 * @param string $icon_name       Icon name including namespace.
+	 * @param array  $icon_properties {
+	 *     List of properties for the icon.
+	 *
+	 *     @type string $label    Required. A human-readable label for the icon.
+	 *     @type string $content  Optional. SVG markup for the icon.
+	 *                            If not provided, the content will be retrieved from the `filePath` if set.
+	 *                            If both `content` and `filePath` are not set, the icon will not be registered.
+	 *     @type string $filePath Optional. The full path to the file containing the icon content.
+	 * }
+	 * @return bool True if the icon was registered with success and false otherwise.
+	 */
+	protected function register( $icon_name, $icon_properties ) {
+		if ( ! isset( $icon_name ) || ! is_string( $icon_name ) ) {
+			_doing_it_wrong(
+				__METHOD__,
+				__( 'Icon name must be a string.', 'gutenberg' ),
+				'7.0.0'
+			);
+			return false;
+		}
+
+		if ( preg_match( '/[A-Z]/', $icon_name ) ) {
+			_doing_it_wrong(
+				__METHOD__,
+				__( 'Icon names must not contain uppercase characters.' ),
+				'7.1.0'
+			);
+			return false;
+		}
+
+		$name_matcher = '/^[a-z][a-z0-9-]*\/[a-z][a-z0-9-]*$/';
+		if ( ! preg_match( $name_matcher, $icon_name ) ) {
+			_doing_it_wrong(
+				__METHOD__,
+				__( 'Icon names must contain a namespace prefix. Example: my-plugin/my-custom-icon' ),
+				'7.1.0'
+			);
+			return false;
+		}
+
+		if ( $this->is_registered( $icon_name ) ) {
+			_doing_it_wrong(
+				__METHOD__,
+				__( 'Icon is already registered.' ),
+				'7.1.0'
+			);
+			return false;
+		}
+
+		$allowed_keys = array_fill_keys( array( 'label', 'content', 'filePath' ), 1 );
+		foreach ( array_keys( $icon_properties ) as $key ) {
+			if ( ! array_key_exists( $key, $allowed_keys ) ) {
+				_doing_it_wrong(
+					__METHOD__,
+					sprintf(
+						// translators: %s is the name of any user-provided key
+						__( 'Invalid icon property: "%s".', 'gutenberg' ),
+						$key
+					),
+					'7.0.0'
+				);
+				return false;
+			}
+		}
+
+		if ( ! isset( $icon_properties['label'] ) || ! is_string( $icon_properties['label'] ) ) {
+			_doing_it_wrong(
+				__METHOD__,
+				__( 'Icon label must be a string.', 'gutenberg' ),
+				'7.0.0'
+			);
+			return false;
+		}
+
+		if (
+			( ! isset( $icon_properties['content'] ) && ! isset( $icon_properties['filePath'] ) ) ||
+			( isset( $icon_properties['content'] ) && isset( $icon_properties['filePath'] ) )
+		) {
+			_doing_it_wrong(
+				__METHOD__,
+				__( 'Icons must provide either `content` or `filePath`.', 'gutenberg' ),
+				'7.0.0'
+			);
+			return false;
+		}
+
+		if ( isset( $icon_properties['content'] ) ) {
+			if ( ! is_string( $icon_properties['content'] ) ) {
+				_doing_it_wrong(
+					__METHOD__,
+					__( 'Icon content must be a string.', 'gutenberg' ),
+					'7.0.0'
+				);
+				return false;
+			}
+
+			$sanitized_icon_content = $this->sanitize_icon_content( $icon_properties['content'] );
+			if ( empty( $sanitized_icon_content ) ) {
+				_doing_it_wrong(
+					__METHOD__,
+					__( 'Icon content does not contain valid SVG markup.', 'gutenberg' ),
+					'7.0.0'
+				);
+				return false;
+			}
+		}
+
+		$icon = array_merge(
+			$icon_properties,
+			array( 'name' => $icon_name )
+		);
+
+		$this->registered_icons[ $icon_name ] = $icon;
+
+		return true;
+	}
+
 	/**
 	 * Modified to also search in icon labels
 	 */
diff --git a/phpunit/experimental/class-gutenberg-icons-registry-7-1-test.php b/phpunit/experimental/class-gutenberg-icons-registry-7-1-test.php
new file mode 100644
index 00000000000000..89696277f4720a
--- /dev/null
+++ b/phpunit/experimental/class-gutenberg-icons-registry-7-1-test.php
@@ -0,0 +1,127 @@
+<?php
+/**
+ * Unit tests covering Gutenberg_Icons_Registry_7_1::register functionality.
+ *
+ * @package Gutenberg
+ */
+class Gutenberg_Icons_Registry_7_1_Test extends WP_UnitTestCase {
+
+	/**
+	 * Registry instance for testing.
+	 *
+	 * @var Gutenberg_Icons_Registry_7_1
+	 */
+	private $registry;
+
+	public function set_up() {
+		parent::set_up();
+		$this->registry = Gutenberg_Icons_Registry_7_1::get_instance();
+	}
+
+	public function tear_down() {
+		$instance_property = new ReflectionProperty( Gutenberg_Icons_Registry_7_1::class, 'instance' );
+
+		/*
+		 * ReflectionProperty::setAccessible is:
+		 * - redundant as of 8.1.0, which made all properties accessible
+		 * - deprecated as of 8.5.0
+		 * - needed until 8.1.0, as property `instance` is private
+		 */
+		if ( PHP_VERSION_ID < 80100 ) {
+			$instance_property->setAccessible( true );
+		}
+
+		$instance_property->setValue( null, null );
+
+		$this->registry = null;
+		parent::tear_down();
+	}
+
+	/**
+	 * Invokes Gutenberg_Icons_Registry_7_1::register despite it being private
+	 *
+	 * @param string $icon_name       Icon name including namespace.
+	 * @param array  $icon_properties Icon properties (label, content, filePath).
+	 * @return bool True if the icon was registered successfully.
+	 */
+	private function register( $icon_name, $icon_properties ) {
+		$method = new ReflectionMethod( $this->registry, 'register' );
+
+		/*
+		 * ReflectionMethod::setAccessible is:
+		 * - redundant as of 8.1.0, which made all properties accessible
+		 * - deprecated as of 8.5.0
+		 * - needed until 8.1.0, as property `instance` is private
+		 */
+		if ( PHP_VERSION_ID < 80100 ) {
+			$method->setAccessible( true );
+		}
+
+		return $method->invoke( $this->registry, $icon_name, $icon_properties );
+	}
+
+	/**
+	 * Should accept valid icon names.
+	 */
+	public function test_register_icon() {
+		$name     = 'test-plugin/my-icon';
+		$settings = array(
+			'label'   => 'My Icon',
+			'content' => '<svg></svg>',
+		);
+
+		$result = $this->register( $name, $settings );
+		$this->assertTrue( $result );
+		$this->assertTrue( $this->registry->is_registered( $name ) );
+	}
+
+	/**
+	 * Provides invalid icon names.
+	 *
+	 * @return array[]
+	 */
+	public function data_invalid_icon_names() {
+		return array(
+			'non-string name'      => array( 1 ),
+			'no namespace'         => array( 'plus' ),
+			'uppercase characters' => array( 'Test/Plus' ),
+			'invalid characters'   => array( 'test/_doing_it_wrong' ),
+		);
+	}
+
+	/**
+	 * Should fail to re-register the same icon.
+	 *
+	 * @expectedIncorrectUsage Gutenberg_Icons_Registry_7_1::register
+	 */
+	public function test_register_icon_twice() {
+		$name     = 'test-plugin/duplicate';
+		$settings = array(
+			'label'   => 'Icon',
+			'content' => '<svg></svg>',
+		);
+
+		$result = $this->register( $name, $settings );
+		$this->assertTrue( $result );
+		$result2 = $this->register( $name, $settings );
+		$this->assertFalse( $result2 );
+	}
+
+	/**
+	 * Should fail to register icon with invalid names.
+	 *
+	 * @dataProvider data_invalid_icon_names
+	 * @expectedIncorrectUsage Gutenberg_Icons_Registry_7_1::register
+	 */
+	public function test_register_invalid_name() {
+		foreach ( $this->data_invalid_icon_names() as $name ) {
+			$settings = array(
+				'label'   => 'Icon',
+				'content' => '<svg></svg>',
+			);
+
+			$result = $this->register( $name, $settings );
+			$this->assertFalse( $result );
+		}
+	}
+}