Stella first appeared internationally at the 1962 Nordic World Ski Championships in Zakopane . There he took 19th place over 15 km and fifth place with the relay. At the Olympic Winter Games in Innsbruck in 1964 , he came in 18th place over 30 km. He had his greatest international success at the Nordic World Ski Championships in Oslo in 1966 . There he won the bronze medal with the relay. He also achieved 21st place over 30 km and 12th place over 15 km. At the 1968 Winter Olympics in Grenoble , he ran in 23rd place over 30 km and 13th place over 15 km. Two years later he came at the Nordic World Ski Championships in Vysoké Tatry on the 27th place over 30 km, on the 17th place over 15 km and on the sixth place with the relay. He completed his last international race at the 1972 Winter Olympics in Sapporo . There he finished 28th over 15 km. At Italian championships he won in 1968 over 15 km, 30 km and with the relay of CS Esercito.
As a ski mountaineer, Stella won the Trofeo Mezzalama in the team in 1971 and 1973 and the Trofeo del Canin in 1962 and 1966.