Mary Jennifer Guinness (née Hollwey; 22 August 1937 – 23 January 2016), was an English-born Irish socialite and member of the Guinness family. She married John Henry Guinness on 9 April 1959, and they had three children: Ian Richard Guinness (b. 15 March 1961), Gillian Sarah Guinness (b. 8 July 1962) and Tania Caroline Guinness (b. 10 February 1966). She was a keen sailor and a member of Howth Yacht Club.