In 2008 he starred as Gavin Cluxton in the television series Fair City. From 2010 to 2012 Macken starred as Sir Gwaine in the TV series Merlin. In 2014 he starred as Dr. TC Callahan in the series The Night Shift. Macken has also starred in the movies Christian Blake, Once Upon a Time in Dublin, Savage, The Rise of the Bricks, Dreaming for You, Centurion, Siren, The Inside, Suspension of Disbelief, Cold, and The Callback Queen. He wrote and directed the films Christian Blake, The Fashion of Modeling, Dreaming for You, The Inside, and Cold.