Mackin started his career with Wrexham in their youth system, before making his first-team debut on the last day of the 2003–04 season. He made 11 appearances the following season and he signed his first professional contract in 2005. He established himself in the team in 2005–06, having made 19 appearances. However, next season, appearances became rarer and in 2008 he was loaned to Conference Premier club Droylsden. After being recalled by Wrexham, he scored in their final match in the Football League before relegation to the Conference Premier. He joined York City on loan in 2009 and played for them in the 2009 FA Trophy Final at Wembley Stadium. After being released by Wrexham he signed for York permanently and played in the 2010 Conference Premier play-off Final at Wembley Stadium. He was released by York in 2011 before having spells with Alfreton Town, Chester, Bangor City, Conwy Borough and Rhyl.