Is it possible to sort the post based on a custom field?

Yes,
You can call action “pre_get_posts”.

add_action('pre_get_posts','search_filter');

You can add parameter :

$args = array(
  'post_status'       => 'publish',
  'posts_per_page'    => 6,
  'paged'             => $paged,
  'meta_key'          => 'event_date',
  'orderby'           => 'meta_value_num',
  'order'             => 'ASC'
);

You can use above parameter e.g. :

function search_filter($query){
    if ( !is_admin() && $query->is_main_query() ) {
        $query->set('post_status', 'publish');
        $query->set('meta_key', 'event_date');
        $query->set('orderby', 'meta_value_num');
        $query->set('order', 'ASC');
    }
}