Born in Halifax, West Yorkshire,[2] on 11 September 1988, O'Brien attended Holy Trinity Senior School in the town.

[3] O'Brien grew up as a Bradford City fan and joined the club's Centre Of Excellence when he was eight-years-old,[2][4] and signed professional terms at the age of 18.

He made his debut for Bradford City as a second-half substitute against Doncaster Rovers on 4 September 2007 in the Football League Trophy.

[9] He played his first game of the 2008–09 season as a second-half substitute against Luton Town, following fellow left-back Paul Heckingbottom's red card.

[12] O'Brien said: "It is great to win an award like this, especially so early in my career, and the fact that it is voted for by supporters makes it that little bit more special.

In May 2009 O'Brien's fine individual effort at Rotherham United was voted Goal of the Season 2008–09 by Bradford City supporters in a recent online poll.

His first appearance of the season came against Sheffield Wednesday on 30 August 2011 coming on for the last 5 minutes of the game, replacing Jack Compton.

O'Brien joined League One side Exeter City on 31 January 2012 for an undisclosed fee as a direct replacement for the departed Scott Golbourne.

[16] On 22 September 2012, O'Brien made his league debut against his former club Bradford City losing 2–0 at the Kassam Stadium, he played 62 minutes, his first competitive game since 10 March.

[19] In August 2014, O'Brien signed for Northern Counties East League Premier Division side Thackley.