One of the few Irishmen playing county cricket, O’Brien was part of his national team that beat Surrey and West Indies during 2004.
A wicketkeeper with attitude, he famously clashed with Windies skipper Brian Lara and he greeted Shane Warne with an attempted reverse sweep the first time the two came into conflict.
But in 2008 O’Brien established himself as a genuine wicketkeeper-batsman, opening the innings for his second county, Northamptonshire.
O’Brien began at Kent, and with Geraint Jones being England's first-choice keeper in 2004/05, O'Brien was given an extended period in the first-team.
He made his LV County Championship debut in 2004 and went on to make 14 appearances, hitting three half-centuries.
He made the same number of first-class outings in 2005 and took 46 catches and five stumpings, as well as hitting 442 runs.
He was banned for one ICC Intercontinental Cup match for a level two breach of the code of conduct following an incident against Scotland in August 2006.
He joined Northants on a one-year deal in 2007 and played in eight championship games, taking 23 catches as he and Riki Wessels competed for the wicketkeeper’s spot.
O’Brien, a generally reliable gloveman, was asked by head coach David Capel to open the batting in all competitions for Northants alongside Stephen Peters.
The move paid off handsomely, with O’Brien scoring 917 first-class runs at 46, with two centuries and five fifties.
He also supplanted Wessels as wicketkeeper, and continued to score heavily for Ireland in Intercontinental Cup and one-day international matches.
County performances were sporadic in 2009 due to international commitments, and was far more effective in limited-overs cricket, making 128 versus Surrey in a NatWest Pro40 match.