Mary Ann O'Brien (born 8 September 1960) is an Irish businesswoman and former politician.

[2] She is the founder and chairman of Lily O'Brien's Chocolates[3] 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.

[4][5] At the launch of Renua in March 2015, O'Brien was announced as a party candidate.

[6] O'Brien clarified that she would remain independent while a Senator and join Renua to stand at the 2016 general election.