Although Bonetto had raced Formula One cars before, he made his World Championship F1 debut in the 1950 Swiss Grand Prix. He was five days short of his 47th birthday. He entered his own Maserati 4CLT in several Grands Prix, under the Scuderia Milano banner, and drove a works Alfa Romeo SpA in 1951, as their number three driver. He shared a third, with Giuseppe Farina in the Gran Premio d'Italia. A move to sports cars followed, but he returned to Formula One at the end of 1952 and had a good season in the Officine Alfieri Maserati in 1953, with a visit to the podium, when he again shared a third-place finish in the Grote Prijs van Nederland. This time partnered by José Froilán González. Away from the World Championship, Bonetto did have some success; he was second in the 1949 in the Gran Premio di Napoli in a Ferrari.