Munn was born in the former Grow Township, now known as Andover, Minnesota. A 1932 graduate of the University of Minnesota, he played guard and fullback for the Golden Gophers under head coach Fritz Crisler. Munn was a two-time first-team All-Big Ten Conference selection and during his senior year in 1931, he served football team captain, was a consensus All-American, and was awarded the Chicago Tribune Silver Football as the Big Ten's best player. Many considered Munn as the top collegiate punter in the nation. He stood just under six feet and weighed 215 pounds, but was recorded running 100 yards in 10 seconds. Munn also served as captain of Minnesota's track and field team.