A native of Detroit, Michigan, McMillan enrolled at the University of Michigan in 1909 and led the freshman football team to an undefeated season, leading to high expectations for the 1910 team under his leadership. In a career shortened by injury, McMillan started only ten games at quarterback, but never lost a game he started. The Wolverines' record in games with McMillan as the starting quarterback was 7–0–3.