Looking around Google for a few minutes yielded several promising results.
Here’s a more detailed one adapted from a snippet on The Code Collective:
function get_user_roles( $user_id ) {
$user_roles = [];
$user = get_userdata( $user_id );
$capabilities = $user->{$wpdb->prefix . 'capabilities'};
if ( !isset( $wp_roles ) ) {
$wp_roles = new WP_Roles();
foreach ( $wp_roles->role_names as $role => $name ) {
if ( array_key_exists( $role, $capabilities ) )
$user_roles[] = $role;
}
}
return $user_roles;
}
This will return an array of the user passed in as $user_id
.