Mark Rudolph MacGuigan PC (17 February 1931 – 12 January 1998) was a Canadian academic and politician.

Born in Charlottetown, Prince Edward Island, the son of Mark Rudolph MacGuigan and Agnes Violet Trainor,^[1] he was educated at Saint Dunstan's University (B.A.), the University of Toronto (M.A., Ph.D. (Philosophy)), Osgoode Hall Law School (LL.B.), and Columbia University (LL.M., J.S.D.) ^[2] He was a professor at Osgoode and the University of Toronto and was dean of law at the University of Windsor.

MacGuigan was elected as a Liberal Party candidate to the House of Commons of Canada in the 1968 general election. He was re-elected in 1972, 1974, 1979, and 1980.

In 1976, he took a turn at provincial politics and ran for the leadership of the Ontario Liberal Party. He lost to Stuart Smith at the leadership convention.

In 1980, he was appointed Secretary of State for External Affairs in the cabinet of Prime Minister Pierre Trudeau. He became Minister of Justice and Attorney General of Canada in 1982.

When Trudeau announced his retirement as Liberal leader and prime minister, MacGuigan ran to succeed him at the 1984 Liberal leadership convention. He placed fifth. He retired from politics following the convention, and became a judge on the federal Court of Appeal.

He died in Oklahoma City of liver cancer in 1998.

• P. Whitney Lackenbauer, ed. (2002). An Inside Look at External Affairs during the Trudeau Years: The Memoirs of Mark MacGuigan. University of Calgary Press. ISBN 1-55238-076-9.