The Tennessee native was signed by St. Louis and debuted with them in 1966. Willis helped the Cardinals to reach the National League pennant in 1967 and 1968, appearing in both World Series. Late in 1969, he was sold to the Astros where he appeared in three games without allowing a run and without earning a decision. Afterwards, he was sent back to the Cardinals.

In 1970, he was sold to the Padres and spent the last year of his big league career with them. Overall, he posted a 11-12 record with 19 saves and a 3.32 ERA in five seasons.

On November 21, 1977, Willis passed away from a malignant brain tumor in Memphis, TN. He was just 34 years old.