His techniques and style of play were emulated by other teams, and his versatility as a pass-rusher and coverage man influenced the development of the modern-day linebacker position.

When he retired, Cleveland coach Paul Brown called him "one of the outstanding linemen in the history of professional football".

[1] Willis was one of the first two African Americans to play professional football in the modern era, signing with the Browns and playing a game in September 1946 along with Marion Motley, a contest which took place months before Jackie Robinson broke the color barrier in the Major League Baseball (MLB) with the Brooklyn Dodgers.

After graduating in 1944, Willis heard about a new AAFC club in Cleveland led by his old Ohio State coach, Paul Brown.

His father died of pneumonia on April 10, 1923,[5] and he was raised by his grandfather and mother amid the financial hardships of the Great Depression.

[3][7] He worried about being compared to his older brother Claude, who had been an All-State fullback at the same school a few years earlier, Willis eschewed the backfield to play tackle and end.

[3] Willis was small for a lineman at 202 pounds, and despite signing up to play for Brown he was initially expected to focus on track and the 60-yard and 100-yard dashes.

[3] Before the following season, scores of Ohio State players left the school to join the military as American involvement in World War II intensified.

[9] Willis volunteered for the U.S. Army, but was classified as 4-F, or only available for service in case of a national emergency, due to varicose veins.

[9] The "Baby Bucks", as they were called, fell to 3–6, although Willis was named a first-team All Conference selection in the Big Ten.

[3][9] By the 1944 season, Brown had joined the military and was coaching a team at Great Lakes Naval Training Station outside Chicago.

[13] The gentlemen's agreement had been in effect ever since segregationist George Preston Marshall entered the league as owner of the Boston Redskins.

[13] In his physical prime but with no real prospect of playing professionally, Willis took a job as the head football coach at Kentucky State College in the fall of 1945.

[15] Willis was about to leave for Montreal when Paul Hornung, a sportswriter for the Columbus Dispatch, called with a message from Brown.

[15] Hornung told Willis to go for a tryout in Bowling Green, Ohio, where the new team, the Cleveland Browns, was holding its training camp.

[19] Willis played middle guard for the Browns, lining up opposite the center but often dropping back into coverage to defend the pass.

[26] Willis and Motley were forced to stay in a separate hotel for a 1949 AAFC all-star game in Houston, Texas.

In a playoff game that year against the New York Giants, Willis caught up with running back Gene "Choo-Choo" Roberts on a breakaway reception in the fourth quarter to prevent the touchdown and ensure a Browns victory.

[31] The 1951 and 1952 seasons were equally successful for Willis, although the Browns lost in the NFL championship to the Los Angeles Rams and Detroit Lions.

[37] Willis's play as a powerful but quick middle guard influenced the development of the modern linebacker position.

"[1] Willis retired because he wanted to concentrate on other activities; he had become a popular figure in Ohio and worked with youth in Cleveland and Columbus.

[38] By the late 1970s, he was the chairman of the Ohio Youth Commission, a state agency created to combat criminality among young people.