Besides being heavyweight champion and his characteristic gap-toothed grin (due to losing two and later all four of his front teeth), Spinks gained notoriety for the disaster which befell his career following the loss to Ali. However, he did challenge once more for the WBC heavyweight title in 1981 (losing to Larry Holmes), and the WBA cruiserweight title in 1986 (losing to Dwight Muhammad Qawi).
As an amateur, Spinks won numerous medals in the light heavyweight division. The first was bronze at the inaugural 1974 World Championships, followed by silver at the 1975 Pan American Games, and gold at the 1976 Summer Olympics; the latter alongside his brother Michael Spinks, who won middleweight gold. Leon would also serve on active duty in the United States Marine Corps from 1973 to 1976.
1974, 1975, and 1976 National AAU light heavyweight champion
Defeated future champion Michael Dokes for first AAU title in 1974
Defeated Abellatif Fatihi (Morocco) KO 1
Defeated Anatoly Klimanov (Soviet Union) 5-0
Defeated Ottomar Sachse (East Germany) 5-0
Defeated Janusz Gortat (Poland) 5-0
Defeated Sixto Soria (Cuba) RSC 3
Spinks debuted professionally on January 15, 1977 in Las Vegas, Nevada, beating Bob Smith by knockout in five rounds. His next fight was in Liverpool, England, where he beat Peter Freeman by a first-round knockout. Later, he saw an improvement in opposition quality, when he fought Pedro Agosto of Puerto Rico and knocked him out in round one. He then fought Scott LeDoux to a draw and defeated Italian champion Alfio Righetti by a decision.
Now a lower ranked contender, he made history on February 15, 1978, by beating Muhammad Ali on a 15-round split decision in Las Vegas. Spinks won the world heavyweight title in his eighth professional fight, the shortest time in history. The aging Ali had expected an easy fight, but he was out-boxed by Spinks, who did not tire throughout the bout. It was one of the few occasions when Ali left the ring with a bruised and puffy face.
Spinks' victory over Ali was the peak of his career. He was the only man to take a title from Muhammad Ali in the ring, as Ali's other losses were non-title contests or bouts where Ali was the challenger. Spinks' gap-toothed grin was featured on the cover of the February 19, 1978 issue of Sports Illustrated.
However, Spinks was stripped of his world title by the WBC for refusing to defend it against Ken Norton, instead agreeing to a return bout against Ali to defend his WBA crown. The title, stripped from Spinks, was then awarded to Norton.
His second match with Ali, at the Louisiana Superdome on September 15, 1978, went badly for Spinks. A now in-shape Ali—with better, sharper tactics—rarely lost control, winning back his title by a unanimous fifteen-round decision. Ali regained the title, becoming the first three-time lineal heavyweight champion. Spinks was never given a rematch; Ali retired after the fight (although he came out of retirement a few years later to fight Larry Holmes and Trevor Berbick).
Spinks's next fight, his only one in 1979, was at Monte Carlo, where he was knocked out in the first round by future WBA world heavyweight champion Gerrie Coetzee. In the following fight, Spinks defeated former world title challenger and European title holder Alfredo Evangelista by a knockout in round 5. He fought to a draw in with Eddie López, in May 1980 he scored a knockout over Kevin Isaac, and in October beat the WBC's top-ranked challenger, Bernardo Mercado, by a knockout in round nine, this fight was on the undercard of Muhammad Ali vs. Larry Holmes.
His strong performance against Mercado earned Spinks a title match against Larry Holmes. In Spinks' only fight in 1981, and what would be his last chance opportunity at the heavyweight title, he had a clear loss by a TKO in the third round at Joe Louis Arena in Detroit on June 12.
It was Spinks' last heavyweight bout for years, as he began boxing in the cruiserweight division. He beat contender Ivy Brown by a decision in ten rounds, and a gained a decision against former and future title challenger Jesse Burnett in twelve rounds.
When his brother Michael Spinks defeated Larry Holmes in a controversial upset for the IBF heavyweight championship in 1985, they became the only brothers to have held world heavyweight championships. They kept the distinction until the Klitschko brothers became champions two decades later.
In the 1980s Leon Spinks competed in several boxer vs. wrestler matches in New Japan Pro Wrestling, including losing by submission to Antonio Inoki. In 1986 Spinks earned his last championship opportunity, fighting Dwight Muhammad Qawi for the WBA cruiserweight championship. Qawi had been defeated by Michael Spinks three years earlier for his WBC light heavyweight championship. However, Leon Spinks lost by TKO in the sixth round. During the fight, Qawi taunted Spinks as he beat him mercilessly in a corner.
Spinks boxed for another eight years with mixed results. In 1994 he lost a bout by KO to John Carlo, the first time a former heavyweight champion had lost to a boxer making his pro debut (promoter Charles Farrell later admitted to falsifying Carlo's record in order to get the fight sanctioned by the District of Columbia). Spinks retired at age 42, after losing an 8-round decision to Fred Houpe in 1995, who was coming off a seventeen-year hiatus.
During the 1990s, Spinks worked for Frontier Martial-Arts Wrestling, winning its world title in 1992, making him the only man to hold titles in both boxing and wrestling. In the late 1990s, Spinks was a headliner on year-round, touring autograph shows.
In 2009 Spinks was featured as part of the 2009 documentary Facing Ali, in which notable former opponents of Ali speak about how fighting Ali changed their lives.
As of 2017, Spinks lives in Las Vegas, Nevada. He told a reporter his life is "comfortable", and that he keeps a low profile.
In August of 2017, Leon was inducted into the Nevada Boxing Hall of Fame along with his brother, Michael.
His son, Cory Spinks, held the undisputed welterweight title and was the International Boxing Federation Junior Middleweight champion in 2006–2008.
In 1990, his son, Leon Calvin, was shot to death in East St. Louis as he was driving home from his girlfriend's house.