Son of an industrialist, Marzotto was best known as the well-dressed racer of his era. In 1950, he drove a Ferrari 195 S to victory in the Mille Miglia road race wearing a double-breasted suit, complete with a tie. Marzotto went on to win the Mille a second time in 1953 where he set the record for average speed in a 340 MM Spider bodied by Vignale. In that same year Marzotto came in fifth overall at the 24 Hours of Le Mans in a 340 MM Berlinetta.
Enzo Ferrari in his book ‘Piloti, che gente’ had this to say about Giannino: “He was an extremely quick driver; a youngster with the character traits of Varzi in the way he could coldly calculate and reason, as well as for his seriousness and grit…Giannino would have been an excellent professional driver – perhaps even a champion.”