Argentine welterweight boxer Mario Guilloti had a lengthy career that saw him win medals at both the Pan American and Olympic Games before becoming the national champion. At the 1967 Pan American Games in Winnipeg Guilloti won the silver medal after losing to Andrés Molina of Cuba in the final. The following year he won bronze at the 1968 Mexico City Olympics before turning professional in 1969. He won his first 15 fights as a pro before losing to Rubén Vázquez Zamora. This was followed by a run of another 18 victories followed by a loss to the Argentine champion Miguel Angel Campanino. Guilloti faced Campanino a further three times, with the last two encounters being for the Argentine welterweight championship. The title fights both took place at Luna Park in Buenos Aires with Campanino winning each time.
From May 1976 to July 1978 Guilloti spent most of his time in Europe, with a lot of his fights taking place in Italy. Of the 18 fights he contested during this period, he won 15 of them, lost two, and drew one. In April 1980 he was 34-years-old when he became the Argentine champion, beating Eduardo Jorge Yanni by knockout at Luna Park. Guilloti won his next two fights, before losing his championship to Alfredo Ruben Lucero, just five months after he had initially won it. He continued to box for three more years, losing his final fight on points in November 1983 at the age of 37. Guilloti fought 102 contests as a professional, winning 73 fights, with 37 of those by knockout.
Argentina