Montermini raced in Formula 3 in 1989, taking second place in the Monaco GP support race and 4th in the Italian F3 Championship. He then moved up to Formula 3000, racing for three season before finally taking second place in the 1992 season, winning three rounds while driving for the Il Barone Rampante team.
He participated in 29 Formula One Grands Prix, debuting on May 29, 1994 for Simtek, replacing Roland Ratzenberger, who had been killed during practice for the 1994 San Marino Grand Prix. Montermini himself crashed heavily in practice for the 1994 Spanish Grand Prix, breaking his left heel and his right foot.
He returned to Formula One the next season, with the Pacific Grand Prix team, and drove for Forti in 1996 alongside countryman Luca Badoer until the team folded. Montermini was also rumoured to become a test driver for the MasterCard Lola team, but it folded after one race in 1997. He scored no points in his Formula One career.
He competed in the American Champ Car series three different seasons: 1993-1994 and 1999. He scored a 4th place at Detroit in his first season, driving for the underfundedEuromotorsport team. In 1999 he drove a few events for Dan Gurney in Gurney’s last season of team ownership. When others such as Alex Barron, Gualter Salles and Raul Boesel were replaced, he filled in and scored a best finish of 11th in Vancouver.
He raced in the 2001 24 Hours of Daytona, but has primarily raced in the FIA GT Championship, mostly in Ferrari cars. He has taken two class wins and four further class podiums. In 2006 he has occasionally raced alongside Jarek Janis and Sascha Bert in a Saleen ran by the Zakspeed team.
In 2007 he won the International GT Open’s GTA class, driving a Ferrari 430 for Scuderia Playteam alongside co-champion Michele Maceratesi, the duo becoming overall champions the following season. He won a second overall championship title in 2013.