Johnson's flamboyance was not only a problem for him in the ring. Not only did he openly enjoy his winnings by opening the cabaret Café de Champion in Chicago, he dared to publicly court white women. Johnson—who married three white women over his lifetime—was denounced on the floor of the United States Senate, and some states passed legislation outlawing interracial marriage based on his case. Reformers during the "white slavery" hysteria managed to have Johnson's liquor license revoked, and also had him charged under the Mann Act, which prohibits transporting women across state lines "for immoral purposes." Johnson had moved across state lines both with his wives and with white prostitutes, but before the Mann Act was enacted. Nevertheless, an all-white jury found him guilty of the offense in May 1913, and he was sentenced to a year and a day in prison.
Rather than serve his prison sentence, Johnson escaped to Europe with his then-current wife, Lucile. He boxed in exhibition matches and performed in vaudeville acts there and in Latin America for two years. In 1915, Johnson agreed to fight the "white hope" Jess Willard for the title. The bout was held in Havana, Cuba, since Johnson could not return to the United States. The boxers fought under a blazing sun for 26 rounds, until Willard knocked Johnson out. Johnson claimed afterward that he had thrown the fight in return for a pledge of amnesty from the United States, but none was forthcoming. He fled back to Europe and lived mostly in Spain, performing in exhibition fights and wrestling matches, acting in a film, and performing as a matador.
In 1920, Johnson returned to the United States and served his prison term in Leavenworth. He worked some odd jobs and spent most of the rest of his life working as a lecturer at Hubert's Museum, a sideshow and penny arcade, on 42nd Street in New York. On June 10, 1946, Johnson was speeding through Franklin, North Carolina, toward the Joe Louis-Billy Conn rematch when his car hit a light pole. He died hours later in a Raleigh hospital.