Mary Ann O'Brien (born 8 September 1960) is an Irish businesswoman and politician. She is the founder and chairman of Lily O'Brien's Chocolates and in 1997, she founded the Jack and Jill Foundation with her husband Jonathan Irwin, to provide home health care to severely sick babies. It was set up as a direct response to their experience of caring at home for their son Jack, born with severe brain damage in 1996. In May 2011, she was nominated by the Taoiseach Enda Kenny to the 24th Seanad. At the launch of Renua Ireland in March 2015, O'Brien was announced as a party candidate. The Sunday Times and the Irish Daily Mail reported that she was not a party member. O'Brien clarified that she would remain independent while a Senator and join Renua to stand at the 2016 general election.