Career
Early career Ger O'Brien was signed by Eric Hannigan before the start of the 2004 season from Athlone Town. He was the first player to represent the Republic of Ireland at any level while playing with Kildare County. He represented the Eircom League International squad in Aberdeen for the quadrangular tournament with England, Scotland and Wales in 2004.
Ger O' Brien made 39 appearances for Kildare County in the 2005 season and was also awarded the clubs player of the season award. Shamrock Rovers Ger left Kildare County for Shamrock Rovers to become one of the country's best full backs. He missed most of the pre-season campaign in his first year with Shamrock Rovers but once the season began he became a first team regular pretty quickly.
He revealed himself to be a tough and uncompromising defender and although he suffered an injury setback in early June he made a quick recovery and picked up where he left off. Derry City Signed for Derry City on three-year full-time deal in February 2009. Played in Derry's four Europa League games in July and August 2009.
Sporting Fingal Following Derry's financial struggles in 2009, he opted to join Sporting Fingal for the 2010 season. . Bohemians After Sporting Fingal ceased trading, O'Brien's contract was cancelled. On the 15, February 2011 Bohemians announced the signing of 9 players including O'Brien.
He made his league debut for his new club against Bray Wanderers on 4 March at the Carlisle Grounds. St Patrick's Athletic O'Brien signed for the club he supported as a boy, St Patrick's Athletic for the 2012 season. He is the club's vice captain and he skippered the side against Cliftonville in the Setanta Cup due to the absence of captain Conor Kenna.
O'Brien started the season off well and after eight league games the Saints defence earned five clean sheets and only conceded three goals. In the 2013–14 UEFA Europa League first qualifying round, O'Brien scored his first goal for the Saints on his 70th appearance when he scored the equaliser in the first leg against VMFD Žalgiris to make it 2–2 in the LFF Stadium in Vilnius, Lithuania. O'Brien represented the Republic of Ireland U23s in the 2007–09 International Challenge Trophy, playing in all three games.
He scored on his third appearance against Belgium. Ireland went on to lose the match 2–1. Club Shamrock Rovers League of Ireland First Division (1): 2006 St Patrick's Athletic League of Ireland (1): 2013 President's Cup (1): 2014 Leinster Senior Cup (1): 2014 FAI Cup (1): 2014 League of Ireland Cup (1): 2015 Maynooth University (As manager) Collingwood Cup (1): 2014 Individual.