Over a 13 year career Willis played for three teams, the Boston Beaneaters (1898-1905), Pittsburgh Pirates (1906-1909) and St. Louis Cardinals (1910), compiling a 249-205 record with a 2.63 ERA. He was known as a workhorse and completed 388 of his 471 starts. He holds the post-1900 records for most losses (29, in 1905) and complete games (45, in 1902) in a single season.
Willis was on one World Series championship team, the 1909 Pirates.
Willis was inducted into the Baseball Hall of Fame in 1995.