O'Brien began his footballing career at Dunfermline Athletic's Academy, but moved to Cowdenbeath in 2003. He signed professional terms in 2007, and after loan spells with Rosyth and Kelty Hearts,[1] he made his first team debut on 7 August 2010, in a 2–0 home loss against Ross County.[2] O'Brien scored his first professional goal on 1 October 2011, in a 1–1 away draw against Arbroath.[3]