Gros was born at Sauze d'Oulx, in the province of Turin in the Piedmont region. He learned to ski at an early age, thanks to Aldo Monaci and Aldo Zulian. At the age of 8, he was for the first time on the podium of local race. Gros made his debut in the World Cup at age 18 in December 1972. In that 1973 season, he won two races in Val d'Isère and Madonna di Campiglio; he was the youngest Italian skier ever to win a World Cup race. Two years later he won the overall title, sharing this result in Italy only with his friend and rival Gustav Thöni and with Alberto Tomba. Thöni had won the overall title the three preceding seasons and would reclaim it in 1975; he was the runner-up in 1974, and if not for Gros, would've won an unthinkable five consecutive overall titles. Gros also won the bronze medal in the giant slalom at the 1974 World Championships in St. Moritz.