After he took part in the Italian Formula 3 and Formula 2 with varying results, he tried in 1977 to start with a purchased Surtees TS19 at the Grand Prix of Italy, but failed to qualify for the race itself. In 1978 he went to Ensign, but left the team again after two more failed qualifications.
Leoni returned to the Formula 2, Formula later emerged from the 3000. In 1986 he founded his own racing team First Racing. The attempt to enter with this team in Formula 1, failed.
Formula 1 Results
Le Mans results
1992 rose Leoni into the speedboat sport. From 1993 to 1998, he started with Italian and from 2003 to 2004 on Monegasque license in the offshore series Class 1, 1997, together with the Italian Edoardo Polli in the boat Bilboa Vice World and European Vice Champion. The same title successes in 2003 he repeated again, back together with Edoardo Polli, this time in the boat Highlander. He won eight Grand Prix races during this time.