Michael Morris Cassidy (born 1937) is a Canadian politician. Formerly a journalist, Cassidy entered politics and was first elected to the Ontario legislature in 1971 representing the Ontario New Democratic Party, Cassidy succeeded Stephen Lewis to become party leader in 1978. He had a difficult job following a charismatic and dynamic figure like Lewis, particularly as Cassidy's personality was rather dry. His leadership in the 1981 Ontario election was uninspiring and voters failed to respond, instead reducing the NDP from 33 seats to 21 seats allowing the Tories to regain their majority government while the Liberals neither gained nor lost seats. Cassidy stepped down as leader and was replaced in 1982 by Bob Rae. Cassidy resigned as MPP in 1984 in order to enter federal politics and was successfully elected to the Canadian House of Commons in the fall of 1984 only to be defeated in 1988.