He was born at Valdagno on 13 April 1928, the son of the king of the Italian wool industry, Count Gaetano Marzotto. Soon after his 20th birthday he entered his father's Lancia Aprilia in the Giro di Sicilia and came in second in his class. In 1950 he and his three brothers, Vittorio, Umberto and Paolo competed in Mille Miglia all driving Ferraris. Marzotto purchased his car based upon his experience driving a similar model at a recent hill climb where he won decisively. Upon testing his new car he found it nothing compared to the previous car. Suspecting some type of deviousness on the part of Ferrari he returned to the factory to confront the old man. Luigi Bazzi, Ferrari's legendary technician was brought in to explain that he had purposely "strangled" the engine in order to protect the young driver to the consternation of all in attendance. Ferrari, somewhat embarrassed promised to personally see that the car would be prepared for the upcoming race.
Giannino was the last to start but would finish first in a double-breasted suit. He won fame not just for winning but for his attire which seemed to catch the spirit of the Italian fans. The young Marzotto decided that for 1951 he would improve upon last year's Ferrari with an all-new design of his own based on the Ferrari 166 with a 212 engine.
In those days before the widespread use of wind tunnels in auto racing builders based their designs on what Marzotto called “optical intuition”. Italy of course is renowned for it’s coach builders and for his new car he turned to Sergio Reggiani & Paolo Fontana of Padua. A low slung body with a rounded shape similar to that of an egg or Uovo in Italian was decided upon. The car went well but retired due to what was thought at the time a problem with the rear axle, In 1953 despite two small crashes Marzotto, who was told in reference to his car by Ferrari to take it or leave it; took it all the way to Brescia for his second victory in the italian classic.
He would later marry with three daughters and until 1969 he headed the family firm. Upon his retirement he devoted himself to sporting hobbies, patronage and hospitality, serving as President of the Mille Miglia Club from 1988 to 1990 and then from 2011 until the time of his death.