Mitchell turned pro in 1981 and captured the WBA and Lineal Junior Lightweight Title in 1986 with a 10th-round KO over Alfredo Layne. He defended the title a record 12 times, and never lost a title fight. In 1991 he also captured the IBF Junior Lightweight Title with a decision win over Tony Lopez (who he'd previously fought to a draw). He retired after the fight, and came back briefly in 1994 for two local bouts, retiring completely in 1995 with a professional record of 45-1-3, avenging his loss and three draws in rematches and therefore being one of the few champions to beat everyone they faced.