Sullivan became the world's Heavyweight champion in 1889, when he knocked out Jake Kilrain on July 8 in round 75 of the scheduled 80 round bout. That fight is considered to be a turning point in boxing's history because it was the last world title fight which was fought under the London Rules and also, the last title fight where gloves were not used.
Sullivan, undefeated up to that point, did not defend his title for the next four years, and he enjoyed the sweet life many champions take after winning the title, becoming a alcoholic, feeling invincible, and getting out of boxing shape.
In 1893, he finally agreed to defend his title, meeting Gentleman Jim Corbett, and he lost by a knockout in 21 rounds, in the first fight under the new Marques of Queensberry rules, and the first title fight held using boxing gloves. Sullivan therefore, became known as the last bare knuckles champion, and the first one to use gloves.
After losing for the first time, Sullivan retired, but he engaged in several exhibitions for the next twelve years.
Sullivan in retirement became a popular stage actor, speaker and bar owner. He is known by autograph experts to have been a good autograph signer, as there are many documents, pieces of paper and photos in existence that are known to have been signed by him. Through the decades, a photo with a facsimile autograph of him has surfaced on books, magazines and novelty stores, and the photo and facsimile autograph are believed to have been a copy of a photo with a real autograph, or perhaps it is a picture taken of the photo with the real autograph. Sullivan's autograph is now valued at hundreds of dollars.
Sullivan ultimately died in 1918, of health problems caused by his drinking problem. He is buried in the Old Calvary Cemetery, in Boston, Massachusetts.
He had a record of 50 wins, 1 loss and 4 draws, with 35 wins by knockout.