Fahey started his professional career as a trainee with Arsenal. He played for Aston Villa, Bluebell United, St Patrick's Athletic and Drogheda United before his transfer to Birmingham City. With Birmingham City he won the 2011 League Cup in England, as well as helping the club gain promotion from the Football League Championship to the Premier League during the 2008–09 season. He left the club at the end of the 2012–13 season, and returned to St Patrick's Athletic for a third spell with the club.