Bill Mitchell moved away from home at the age of 16 to play for the Stratford Kroehlers in 1946-47. He stayed with the team for two years and also played two games with the Kitchener Dutchmen before returning to Stratford for a third year. During his final year of junior eligibility in 1949-50, Mitchell played with the Toronto Marlboros.
At 20, he played semi-pro hockey with the Halifax St. Mary's and the Moncton Hawks in eastern Canada before returning to Ontario where he played two seasons with the Kitchener Dutchmen of the OHA senior league.
Beginning in 1952-53, Mitchell began a seven year association with the IHL's Toledo Mercurys. He left the team in the fall of 1962 to play for the Windsor Bulldogs of the OHA senior league and the team advanced to the Allan Cup. He also represented Canada at the 1962 World Championships.
Mitchell, a member of the NHL's One Game Wonder Club, played his lone game with the Detroit Red Wings during the 1963-64 season after signing a free-agent contract with the team on February 22, 1964. Although the game and his performance as a whole was rather uneventful, it was certainly the highlight of his career, getting to play with the likes of hockey legends Gordie Howe, Alex Delvecchio and Norm Ullman.
In 1966-67 he took a year off from playing to coach the University of Toledo in the NCAA. At the end of the school season he did dress for seven games with the Toledo Blades where he remained for three years. In 1969-70, Mitchell took on the unique dual role of player/coach while with the Blades. Mitchell continued to play hockey with an assortment of minor-league teams until retiring in 1973 at the age of 43.