Killian Brennan (born 31 January 1984 in Drogheda) is an Irish football player.
Noted for his wing play and ability to fire in accurate crosses, Brennan was signed by Peterborough United in his teenage years. In 2004, he was capped several times for the Republic of Ireland under-19s, before moving back to play in the League of Ireland.
He was signed by John Gill for Dublin City, however, less than a year later, newly appointed boss Roddy Collins' 'purge' of the club meant that Brennan was deemed surplus to requirements. Immediately snapped up by Stephen Kenny for Derry City for the 2004 season, the player was a revelation and made the left wing spot at The Brandywell his own after having made his debut in a home game against St. Patrick's Athletic on 23 September 2004. He has also been deployed to fill in at left full-back on occasion. In the 2006 season he played in their UEFA Cup run in wins over IFK Göteborg and Gretna FC and helped Derry to the FAI Cup and League of Ireland Cup.
It is this abundant talent that attracted the attention of his hometown club, Drogheda United who declared their interest in Brennan following the end of the 2006 season. However, it was Bohs who captured his signature, signing the winger on a free transfer.
Brennan scored his debut goals for his new club in United Park versus his hometown club, netting a freekick and a penalty in a 2–1 win for Bohs. He continued his good form netting 5 times in May 2008 and this did not go unnoticed as he was awarded Soccer Writers' Association of Ireland player of the month for May. Killian's goals helped Bohs blow away the competition as they marched to the 2008 League of Ireland title and his form was rewarded when he was voted on to the League of Ireland Premier Division Team for 2008, receiving a staggering 86% of the votes for the left midfield position.