Career
O'Neill started rowing while in New Zealand but returned to Ireland in 2008 to try and secure a place in an Irish crew. He competed for Ireland from 2006–2008. He returned to New Zealand in 2009 and competed for New Zealand from 2010–2012 after which he retired from international competition.
O'Neill competed in the mens coxless four at the 2008 Beijing for Ireland finishing in tenth place. He competed in the 2012 London in the mens coxless four for New Zealand finishing eleventh.