The 25 year old former Blackrock College student played for UCD before making his Leinster debut in 2006. He went on to earn 12 caps before moving to Ulster in 2007 where he appeared 15 times for the Province.
Cillian arrived in Galway in time to join the squad and fellow scrumhalves Frank Murphy and Conor O'Loughlin on their trip to the Aran Islands where they are undergoing pre-season training under the supervision of Director of Rugby Eric Elwood, Assistant Coach Dan McFarland and new coaches Brian Melrose and Mike Forshaw.