As a youngster he learned Great Highland bagpipes.
He became a member of Green Fields of America in the 1980s, rubbing shoulders with Seamus Egan, Eileen Ivers and Mick Moloney.
He has appeared on over 90 albums, including Dolly Parton's Heartsongs: Live from Home, Susan McKeown's Bones, and two albums by Eileen Ivers – Wild Blue (1996) and Crossing the Bridge (1999).
He has recorded five solo albums, including The Invasion in 1987, The Gift in 1998, and O'Sullivan Meets O'Farrell in 2005.
O'Sullivan Meets O'Farrell: Volume II was recorded in February 2008 in Newport, Rhode Island, with baroque cellist Audrey Sabattier-Cienniwa and harpsichordist Paul Cienniwa playing basso continuo.