Biaggi came to competitive racing relatively late, making his first motorbike appearance in 1989 at age 18. He won the Italian Sport Production Championship in 1990 and progressed to the 250cc World Championship via the European 250cc title in 1991 riding an Aprilia RS250. He took his first 250cc Grand Prix win at Kyalami in 1992, added a single win at the European Grand Prix in Barcelona in 1993 while riding for Honda, then returned to Aprilia and utterly dominated the class.
Between 1994 and 1996 Biaggi won three consecutive 250cc world titles on Aprilia machinery — his black Chesterfield-liveried bike one of the most recognisable in the class. He made the unusual choice to leave the championship-winning Aprilia for 1997 and rejoin Honda's Kanemoto squad, winning his fourth consecutive 250cc title and equalling Phil Read's record of four 250cc world championships.
Biaggi moved to the 500cc class in 1998 with Kanemoto Honda, winning his debut race at the Japanese Grand Prix at Suzuka and adding a second victory at the Czech Republic Grand Prix. He led the championship with three rounds remaining before being controversially disqualified at the Catalan Grand Prix after crossing the line first — a stop-and-go penalty for an alleged yellow-flag infringement which he had not served — costing him the title to Mick Doohan. He finished second overall.
He joined the Yamaha factory team from 1999, finishing third in 2000 and coming closest to the MotoGP title in 2001, when he was again runner-up to Valentino Rossi after crashing from the lead at the Czech Republic Grand Prix at Brno while trailing Rossi by just ten points. He finished second again in the inaugural four-stroke MotoGP season in 2002, winning at Brno and Sepang despite Yamaha's slower start to the year.
Biaggi switched to Camel Honda in 2003 and finished third in both 2003 and 2004, winning races at Silverstone and the Pacific Grand Prix in 2003. He joined the factory Repsol Honda team for 2005 but recorded no wins and finished fifth. Honda effectively blocked him from continuing in MotoGP for 2006, ending his premier-class career.
Biaggi signed with Corona Alstare Suzuki for the 2007 WorldSBK season, winning his debut Superbike race at Losail — becoming the only rider to win on debut in both the 500cc class and WorldSBK. He finished third overall. After a difficult 2008 season on a satellite Ducati, he joined the returning factory Aprilia team in 2009, a year primarily devoted to developing the RSV4.
The breakthrough came in 2010 when Biaggi won Aprilia's and Italy's first Superbike World Championship title. A foot injury disrupted 2011 and he finished third. He reclaimed the championship in 2012 in a narrow victory over Tom Sykes — and promptly retired from full-time competition at age 41, the oldest WorldSBK champion in history.
Biaggi's rivalry with Valentino Rossi is one of motorcycle racing's most discussed, spanning the 500cc and MotoGP eras from 2000 to 2005. He finished behind Rossi in every season they competed together directly. His rivalry with Mick Doohan in 1998 was equally intense and produced public disputes around the Catalan disqualification. He was nicknamed the "Roman Emperor" and "Mad Max" for his combative personality and difficult relationships with media and fellow riders. He was engaged to television personality and Miss Italia 2002 winner Eleonora Pedron, with whom he has a daughter and a son.
In 2020, Biaggi was named a FIM Road Racing Legend, and in 2022 was inducted into the MotoGP Hall of Fame. Between 2019 and 2022 he owned a Moto3 racing team based in Monaco.
Biaggi's 13 premier-class victories, 58 podiums, and 23 pole positions make him statistically one of the most accomplished riders never to win the MotoGP World Championship. His six world titles across two disciplines and his 2012 WorldSBK title at age 41 cement a legacy of sustained excellence across more than two decades at elite level.