A Queensland State of Origin representative forward, he played club football in Australia for the Sydney Roosters, South Queensland Crushers, Gold Coast Chargers and Newcastle Knights (with whom he won the 2001 NRL premiership), as well as English club Wakefield Trinity Wildcats.
[3] O'Brien made his first grade debut for Eastern Suburbs against St. George in round 12 of the 1993 NSWRL season.
In 1996, O'Brien joined South Queensland and in 1997 played in the club's final ever game, a 39–18 victory over Western Suburbs.
He played for the Newcastle Knights from the interchange bench in their shock 2001 NRL Grand Final victory over the Parramatta Eels.
Having won the 2001 NRL Premiership, Newcastle travelled to England to play the 2002 World Club Challenge against Super League champions, the Bradford Bulls.