Early career Born in
Johannesburg, South Africa, O'Brien started his career at Scottish club
St Mirren, where he progressed through the youth ranks, before making his debut as a 16-year-old during season 1997–98. After only just reaching double figures in appearances for the first-team, he was sold to
Blackburn Rovers for a fee of around £300,000 in 1999. O'Brien moved back on loan for the rest of the season, and scored his first and only goal for St Mirren with a free-kick against
Hamilton Academical. He made only one first-team appearance for Blackburn Rovers during his time at
Ewood Park in an
English League Cup match against
Portsmouth before leaving the club for
Livingston in 2002. O'Brien blamed his lack of first-team action on a clause in his contract, saying that a league appearance would mean Blackburn had to pay St Mirren an extra £300,000.
Livingston In September 2002, O'Brien moved back to Scotland after
Scottish Premier League side
Livingston agreed a deal to sign him and his teammate
David McNamee from Blackburn Rovers. In 2004, he helped Livingston to their first major national honour by becoming an integral part of the
Scottish League Cup winning side on 14 March 2004. O'Brien's excellent form for Livingston saw him attract interest from other clubs such as
Aberdeen,
Hearts and clubs south of the border. In total he made 119 league appearances for Livingston in all competitions and scored 16 goals.
Sheffield Wednesday On 14 July 2005, O'Brien signed for
English Championship side
Sheffield Wednesday on a three-year contract after the midfielder rejected a new contract offer from Livingston.
Falkirk O'Brien returned to Scotland once more by signing for
Falkirk. He scored his first and what turned out to be only Falkirk goal in a 4–1 win over
Hamilton on 27 September 2008. He spent three seasons at Falkirk before being released in 2011.
Return to Livingston After a one-year absence from the game, O'Brien spent a trial period with
Airdrie in August 2012. Despite the
North Lanarkshire club keen to secure his services, O'Brien moved on and returned to his former club
Livingston. Initially, O'Brien played as a trialist in the club's reserve matches to regain his fitness before signing a short-term contract on 22 November 2012. He made his second debut for Livingston on 17 November 2012 in a 2–1 home win over his former club Falkirk. After the expiry of his contract at the end of December 2012, he signed on again until the end of the season. A stand out performer for the club during his first season back, he was voted Livingston's 2012–13 Player's Player of the year. On 4 June 2013, O'Brien signed a new two-year contract with the club, keeping him at
Almondvale until the summer of 2015.
Alloa & Cowdenbeath After three seasons with Livingston, O'Brien transferred to
Scottish Championship rivals
Alloa Athletic in June 2015 where he spent one season before moving to
Scottish League Two side
Cowdenbeath. After a season with Cowdenbeath, O'Brien announced his retirement from football at the end of the 2016–17 season. ==Coaching career==