Background
O'Brien was born in Dublin and raised in the Ballyfermot district.
O'Brien was born in Dublin and raised in the Ballyfermot district.
He made his debut in the Football League for Bradford City in August 2009. He has represented Ireland at all levels up to under-19. O'Brien began his football career with Ballyfermot club Cherry Orchard.
In the summer of 2006 he moved to England to take up a scholarship with Birmingham City. After only one year with the club, during which he was part of the youth team which reached the quarter-final of the FA Youth Cup, he signed a two-year professional contract. O'Brien joined Conference North side Solihull Moors on a month's loan in January 2009, but the loan was interrupted when the player sustained a pelvic injury a couple of weeks later.
After his contract with Birmingham expired, O'Brien spent pre-season with League Two club Bradford City, he impressed during trials scoring on his debut in a pre-season friendly against Burnley, and on 4 August 2009 signed a three-month contract. He made his professional debut for Bradford on 12 August as a second-half substitute in a 3–0 loss against Nottingham Forest in the League Cup. His debut in the Football League came three days later as a late substitute in the goalless draw at home to Port Vale.
O'Brien scored his first goal for Bradford on 22 August, in a 5–4 victory away at Cheltenham Town. Due to having surgery O'Brien has been restricted to substitute appearances. O'Brien signed a new 18-month contract with Bradford City on 29 October, but was released on 26 July 2010, 10 months early.
He subsequently returned to his native Dublin where he signed for his boyhood club St Patrick's Athletic. He signed for Longford Town in July 2011. He was released in July 2012.
In July 2013 he was playing for Athlone Town. He signed for Bohemians ahead of the 2015 season. While a Cherry Orchard player, O'Brien captained Ireland's under-16 side.
He graduated to the under-17s, missing out on the elite qualifying round of the 2007 UEFA Under-17 championships through injury, under-18s, and, in the 2008–09 season, to the under-19s.