Mayorga, who enjoys lighting up a cigar everytime he wins a fight and who is a confessed smoker of two packs of cigarettes a day when he is not doing his boxing training, is also the first Costa Rican to win a world boxing title, because, apart from being Nicaraguan, he also became a Costa Rican when he obtained Costa Rican citizenship in the 1990s.
Mayorga stepped into professional boxing with the wrong foot, being beaten by a knockout in six in his first professional bout by Humberto Aranda in 1993.
Sad but otherwise undaunted by defeat, he came back in 1994 to win three fights, all by knockout, including the third round knockout win over Jose Morales, which was his first career win.
His first fight in 1995 was also his first fight in Nicaragua, and it was fought for the Nicaraguan Welterweight title. Mayorga won the title when he knocked out Miguel Perez in six rounds. After two more knockout wins, he defended it in a rematch with Perez, and the second time, he defeated Perez by a knockout in three.
He then took off three years from boxing, and when he returned, in 1998, he beat German Espinales by a knockout in four, but in his next bout, he lost a ten round decision to former Edwin Rosario rival Roger Flores. After the Flores bout, he fought Henry Castillo and suffered his second loss in a row, also by decision in ten. So far, he hasn't lost another bout.
In his next fight, in 1999, he beat Porfirio Miranda by a knockout in one round. After one more win, he gained revenge against Castillo, defeating him by a knockout in seven, and then he met Jose Cordova for the Central American Welterweight title. He added that belt by beating Cordova by a decision in twelve.
After one more win, Mayorga went to Puerto Rico to meet Cuba's fringe contender Dyobelis Hurtado, a boxer who had faced Pernell Whitaker and Kostya Tszyu in world title tries, among others. Mayorga and Hurtado came up with a technical draw in two rounds, and in his next fight, Mayorga lifted the WBA's Latin American Jr. Middleweight belt with a two round knockout of Marcos Avendano. A rematch with Espinales for the Fecarbox Welterweight title, brought Mayorga exactly the same result as their first encounter: A four round knockout win, and another minor title belt.
He won seven more fights in a row, including 2 defenses each of his WBA Latin American and Fecarbox belts, until, on July 28 of 2001, he challenged the WBA's world Welterweight champion Andrew Six Heads Lewis at the Los Angeles Roy Jones Jr-Julio Gonzalez undercard. The fight was declared a no contest after two rounds because both fighters had cuts opened by a headbutt and they were unable to continue. However, they had a rematch on March 3 of 2002 and Mayorga made history, becoming the first Costa Rican world champion ever, and the fifth Nicaraguan to win a title, by knocking Lewis out in five rounds.
Despite winning the title and achieving those accomplishments, Mayorga was still not considered to be the real champion in the division by most experts: Vernon Forrest, who had taken the WBC's world Welterweight championship from Shane Mosley and defeated Mosley again in a rematch, was considered by many to be one of the best fighters, regardless of fighting division, around the world.
Mayorga and Forrest quickly signed up for an unification bout, and on January 25, and in front of an HBO Boxing audience, Mayorga upset most boxing critics and experts by dropping Forrest in round one, and once again in round three, winning the fight by a knockout in the third, and becoming the WBA and WBC's undisputed world champion.
On July 12, also in front of an HBO boxing audience, Mayorga and Forrest had a rematch, and this time Mayorga retained the title by a 12 round majority decision.
A woman in Managua accused Mayorga, on July 26, of hitting her after she allegedly tried to collect a debt of 7,500 dollars on friday, July 18. Mayorga says he wasn't in Managua that day; he said he was in El Sauce.
Mayorga will visit Iraq soon, to do a boxing exhibition tour in front of United States military personnel.
Mayorga was featured for the first time on the cover of Ring Magazine on the December 2003 issue, released in October. The cover read The craziest man in the sport: Mayorga lights up boxing.
On December 13, Mayorga lost his world titles, to Leon Spinks' son, Cory by a majority decision in Atlantic City.
Mayorga's record stands at 26 wins, 4 losses and, 1 draw and 1 no contest, with 23 wins coming by knockout.