He had a mark of 14 wins and no losses with seven knockouts - including victories over former Olympic Games bronze medalist Aristides Acevedo and over Dana Roston - when he met a former or future world champion for the first time inside a ring.
After six more wins in a row, including one over future world champion Terron Millett, Mitchell fought for the WBC continental Americas light welterweight title in Dallas, Texas on April 11, 1996.
On May 10, 1997, Mitchell defeated Jose Rafael Barboza by a twelve-round decision in Miami, Florida to win the WBA's Fedelatin belt in the same weight division.
On October 10, 1998, he beat Moroccan Khalid Rahilou by a twelve-round unanimous decision in Paris, France, becoming the WBA light welterweight champion.
Mitchell retained his world title four times, his last successful defense being against Puerto Rican Felix Flores on September 16, 2000, at Las Vegas.
After that fight, demand rose for a unification title bout between Mitchell and Kostya Tszyu of Australia, the WBC light welterweight champion.