His career record in singles on the ATP Tour was 199–218, winning two titles - at Newport, Rhode Island in 1978 and San Jose, California in 1979.

His doubles record was 210–191, and he won nine titles: Auckland (1979); Stowe, Vermont and Cologne (1980); Richmond WCT (1981); Johannesburg (1981); Tampa (1981); Columbus, Ohio (1982); Ferrara (1983); and La Quinta, California (1984).

He was the runner-up in eight tournaments: Sarasota, Florida (1978); North Conway, New Hampshire (1978); Rotterdam (1979); Maui, Hawaii (1982); Ancona (1982); Toulouse (1983); Florence (1984); and Queen's Club (1984).

Mitton had career wins over John McEnroe, Jimmy Connors, and Arthur Ashe in singles.

In his first Grand Slam tournament in 1973, he reached the fourth round of Wimbledon, then lost to Connors in straight sets.