He specializes in religious affairs and was Northern correspondent of The Irish Catholic until he started work on "In Good Time".
He left the BBC on 31 March 2013, having been on the staff for 28 years, and has established his own business, Martin O'Brien Media, based in Belfast.
[5] He is Associate Producer and originator[6] of "Our Man in the Vatican"[7][8] the 2010 BBC (Northern Ireland) TV observational documentary trilogy depicting a year in the life of Francis Campbell,[9][10] then United Kingdom Ambassador to the Holy See - and its sequel "Our Man in the Vatican: The Papal Visit" which was broadcast shortly after the Pope's visit to Britain.
[11] In March 2013 O'Brien covered the Conclave and the election of Pope Francis for BBC Radio Ulster and broke the news of the election live on BBC Radio Ulster's Evening Extra programme as the white smoke bellowed from the chimney of the Sistine Chapel, ahead of numerous other news outlets worldwide.
In an article for BBC News On-Line he reported that the Irish Government will eventually re-open an Embassy to the Holy See.