He had a promising start, finishing third in his first race with Massimo Ciccozzi's team Scuderia del Passatore at Autódromo do Estoril.

In 1977 Leoni made his Formula One debut with Surtees at the 1977 Italian Grand Prix, replacing Vern Schuppan, but failed to qualify.

Leoni qualified for the opening event, the 1978 Argentine Grand Prix, but was forced to retire the car after 28 laps because of an engine failure.

After failing to qualify the car in the following two races in South Africa and the United States, Leoni departed from the team and was replaced by Jacky Ickx.

Following a few moderately successful seasons, with wins for drivers Marco Apicella and Pierluigi Martini, in 1989 Leoni made an abortive attempt to enter Formula One with a car designed by Richard Divila and Gabriele Tarquini at the wheel.