St Patrick's Athletic F.C.
O'Brien is a left winger with plenty of speed and trickery. He was an integral part of Galway United's first season back in the Premier Division in 2007. So much so that he was elected to the PFAI Premier Division Team of the Year and he was subsequently voted Galway United player of the year for 2007. He also won the Galway United Supporter's Trust (GUST) 2007 player of the year award. O'Brien was subject to interest from Derry City who are believed to have offered him an excellent deal, however he opted to commit himself to the Tribesmen for another season at least. In July 2008 he signed for St Patrick's Athletic F.C. from Galway United. He stayed at St Pats for one season before returning to Galway United in January 2009.