Early comic influences included W. C. Fields, Laurel and Hardy, and particularly Richard Pryor: "It was also poignant and heartfelt and I realised then that stand-up could be an art-form".

[2] He briefly attended Queen’s University in Belfast studying English, but dropped out and worked various menial jobs in Italy, Amsterdam, and finally London at age 21.

[1] O'Neill is a veteran of the Edinburgh Fringe Festivals, having performed stand-up or theatre gigs there for over twenty years.

As a writer, his debut feature film Arise and Go Now was screened by BBC2 and was directed by Danny Boyle and starred Ian Bannen.

Charles Isherwood of The New York Times praised the effective writing and O'Neill's performance as "hold[ing] the attention fast with its understated, almost offhand intensity.".