He played as a midfielder notably in the Premier League for Aston Villa, Bolton Wanderers and Everton.
He won promotion back to the Premier League with Bolton in 2001, scoring the opening goal for them in the play-off final,[4] but then fell out of favour.
He was sacked on 30 August 2006 following Bohemians' elimination from the FAI Cup at the hands of Shamrock Rovers, in which he missed a penalty late in the game.
On 15 February 2007, he agreed to sign for Eircom League of Ireland Premier Division side Cork City on a two-year contract.
Farrelly was however not allowed to play for Cork until 1 July 2007 as FIFA regulations at the time allowed players to play professionally for a maximum two clubs in the period between 1 July of one year and 20 June of the next (see FIFA Two for an explanation on this case and an ensuing amendment to the regulation in question:).
His manager Alan Matthews reported: "Gareth has had major surgery and remains in intensive care in Warwick hospital."