Born in
Dublin, Farrelly played schoolboy football for
Bohemians F.C. Aston Villa signed him as a 16-year-old in 1992, and he made his Villa debut on 20 September 1995 against
Peterborough United. Farrelly moved to
Everton in July 1997 for approximately £700,000, and after a season where Everton, and Farrelly personally, struggled, he scored the goal (ironically with his weaker right foot after numerous wayward efforts with left foot throughout the season) that preserved their Premier League status on the final day of the 1997–98 season against
Coventry City. Farrelly then underwent a trial with
Leicester City. He left the Foxes after they ended their interest in him. On 24 November 2006, he joined
Blackpool on a short-term contract, which expired in February 2007. 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:). On 12 May 2008 Farrelly underwent a serious operation to remove a tumour from his pancreas. His manager Alan Matthews reported: "Gareth has had major surgery and remains in intensive care in Warwick hospital." The operation was an apparent success. Following his illness he had spells at
Morecambe and
Warrington. Farrelly settled a case against Cork City for unfair dismissal in October 2009. ==International career==