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 club's 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. On 11 November2007 Ger was voted Shamrock Rovers Player of the Year for the 2007 season and on the 13th he also represented his country in an Under 23 international against Slovakia in Dalymount Park.
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.
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.
International career
O'Brien represented the Republic of Ireland U23s in the 2007–09 International Challenge Trophy, playing in all three games. He won his first cap against Slovakia on 13 November 2007 and then earned a second cap in May 2008 against Northern Ireland. He scored on his third appearance against Belgium. Ireland went on to lose the match 2–1.
Coaching career
O'Brien dipped his toe into coaching while still a player at St Patrick's Athletic. He coached NUI Maynooth to Collingwood Cup glory for the first time in their history in 2014 by defeating NUI Galway in the final. In 2014, O'Brien was appointed as Director of Football for the schoolboys section at St. Francis.The club won two All Ireland trophies in his time and 7 players were transferred to the UK. In November 2016, O'Brien progressed to being appointed as Director of Football for the underage teams at St Patrick's Athletic, he would also take up a coaching position with the first team while continuing to play. Since taking over the role as Director of Coaching, St Patrick's Athletic have had unprecedented success at academy level. In 2019 the club won 6 trophies in total with doubles at U13 & U15s age groups respectively. Not only has success come in the form of trophies its also come with players representing Ireland across all underage levels. Over 25 players have been capped since O" Brien took the role. In 2020 O'Brien graduated with the highest possible honour to complete his UEFA Pro Licence course.
