Michael Spinks turned professional with a win over Eddie Benson, knocked out in one round on April 17, 1977 in Las Vegas. With that, Spinks began a 31 fight winning streak that would almost extend to the end of his career. After four more wins, Spinks finished '77 with the first fight that began a gradual ascent in opposition quality: an eight-round decision over Gary Summerhays, a popular young boxer of the time. In 1978, Spinks won two fights, including an eight-round decision over former world Middleweight title challenger Tom Bethea, in the same undercard where his brother Leon dethroned Ali as
Michael Spinks and narrow fifteen-round unanimous decision and becoming the first ever world light-heavyweight champion to win the world heavyweight title. His controversial victory over Holmes was named "Ring Magazine" Upset of the Year. With this, Michael and Leon had also become the first pair of brothers ever to be world heavyweight champions, followed two decades later by Wladimir and Vitali Klitschko. In 1986, Spinks and Holmes fought a rematch as part of the heavyweight unification series, and had nearly the same result, this time Spinks winning by a 15-round split decision. After that, he retained the world heavyweight championship once again,