Born in Columbus, Ohio, Willis attended Ohio State University, where he joined the track and football teams. He was part of a Buckeyes football team that won the school's first national championship in 1942. After graduating in 1944, Willis heard about a new AAFC club in Cleveland led by his old Ohio State coach, Paul Brown. He got a tryout and made the team. With Willis as a defensive anchor, the Browns won all four AAFC championships between 1946 and 1949, when the league dissolved. The Browns were then absorbed by the NFL, where Willis continued to succeed. Cleveland won the NFL championship in 1950.