McMackin was one of the stars in early UT Martin Junior College history.
As a two-year member of the UTMJC teams, he played end. The 1936 team went undefeated and McMackin earned All-Mississippi Valley Conference honors. The 1936 team outscored its opponents 228-22. Following his two years in Martin, he and seven Martin teammates went to Memphis State to form the nucleus of the only unbeaten Memphis State team in history.
He later enjoyed an outstanding service record in the US Navy, receiving numerous honors and attaining the rank of Lt. Commander. He stayed active in the reserves until 1960, retiring as a Commander.