The Tuscan, who only a week ago presented a book about his sporting achievements, won the Giro D'Italia in 1948, 1951 and 1955.
Magni, who joined Mussolini's National Fascist Party in 1943, was the 'third man' of the golden age of Italian cycling at the time of the rivalry between Gino Bartali and Fausto Coppi.
"It is with immense sorrow that the Italian Association of Professional Racing Cyclists says goodbye to Fiorenzo Magni," the body said in a statement.
"A great champion and man, and one of the founders of this association in 1946. (We) say goodbye with tears in our eyes, thanking him for what he succeeded in doing."
Magni was president of the association between 1969 and 1982.
He had his best chance to win the Tour De France in 1950, but was forced to retire during the 12th stage while wearing the yellow jersey.
Bartali insisted the entire Wilier Triestina team retire after he had been attacked by angry French fans on Col d'Aspin convinced he had caused the fall of Jean Robic.
Magni will arguably best be remembered for an extraordinary act of bravery on the 1956 Giro when he broke his collarbone and carried on racing.
Tying a rope to his bike and holding it with his teeth in order to give himself pedalling leverage, he amazingly finished second overall.
A controversial figure, Magni was accused of cheating his way to his first Giro victory.
Weak on the big mountain climbs, he was docked two minutes for being helped up the Pordoi mountain stage amid claims fans had been strategically placed to push him up the hill.
Despite the punishment, Magni still had possession of the pink jersey, Coppi withdraw himself from the race in protest, while Magni was booed as he crossed the line.
Magni was banned from cycling in 1946 and subsequently put on trial for allegedly fighting partisans during the so-called "massacre of Valibona" in Tuscany.
He denied any part in the killings, though admitted to being a part of a fascist militia. Magni was acquitted of the charges.
- Fiorenzo Magni
- Fausto Coppi
- National Fascist Party
- Gino Bartali