Michael Grattan O'Leary (February 19, 1888–April 7, 1976) was a Canadian journalist, publisher and a member of the Senate of Canada.
He spent two years at sea before entering journalism with the St. John Standard.
He ran as a Conservative Party candidate in the federal riding of Gaspé in the general election of 1925 but was defeated.
He was a confidant of a number of prime ministers, including Arthur Meighen and John Diefenbaker.
He also served as the rector of Queen's University in Kingston, Ontario in 1968 but was forced to resign under student pressure.