O'Brien is a trained teacher. In the late 1980s, he went back to his old school to teach there. He also taught at an intermediate school in Auckland. He moved to England in the early 1990s where he worked as a teacher and coached rowing at Latymer Upper School, Hammersmith. He worked closely with the Latymer Upper School boatman at the time, Coyne T. Mullen. In 1999, he went on to Shiplake College, on the River Thames south of Henley-on-Thames; he was the deputy headmaster there. One of the Shiplake College rowers who had trained under him, Will Satch, went to win Olympic bronze at the 2012 Summer Olympics (coxless pair) and gold four years later (eight). Before he left Shiplake College, a new coxless four boat purchased by the school was named for O'Brien. He became headmaster of Jumeirah English Speaking School (Dubai, UAE) in mid-2011, and director in September of 2019.