Born in
Saint Paul,
Minnesota, MacKinnon received a
Bachelor of Laws from
University of Minnesota Law School in 1929. MacKinnon was a member of the editorial board of the
Minnesota Law Review and played as a center on the
Golden Gophers football team. MacKinnon was also an
All-American
javelin thrower for the
Minnesota Golden Gophers track and field team, finishing 5th at the
1928 NCAA Track and Field Championships. He was an assistant counsel for Investors Syndicate (now a component of
Ameriprise Financial) of
Minneapolis, Minnesota from 1929 to 1942. He was a member of the
Minnesota House of Representatives from 1935 to 1942. He was in the
United States Navy as a Commander from 1942 to 1946. MacKinnon was elected as a
Republican to serve as a
United States representative for the Third District of Minnesota to the
80th congress (January 3, 1947 – January 3, 1949), but was defeated when he sought re-election. He served on the
Education and Labor Committee. He was in private practice of law in Minneapolis from 1949 to 1953. He was the
United States Attorney for the District of Minnesota from 1953 to 1958. In
1958, he ran as the
Republican nominee for
governor of Minnesota and lost the general election to
Orville Freeman. He was in private practice of law in Minneapolis from 1958 to 1960. He was a Special Assistant United States Attorney General from 1960 to 1961. He was general counsel and vice president for Investors Mutual Funds of Minneapolis from 1961 to 1969.
Notable cases During his service as United States attorney, MacKinnon successfully prosecuted the first labor case under the
Taft-Hartley Act against
Archer Daniels Midland, Gerald Connelly, and Sidney Brennan in
United States v. Gerald Connelly. During his service as Special Assistant United States Attorney General in 1960, MacKinnon focused on labor racketeering investigations involving James Hoffa. MacKinnon started the Test Fleet investigation that led to James Hoffa's conviction for perjury. ==Federal judicial service==