Tarquini began competitive karting in 1976. By 1985 he was racing in Formula 3000 with underfunded teams, his best result being a second place at Imola in 1987. That same year he made his Formula One debut in a one-off drive for Osella at the San Marino Grand Prix.
He joined Coloni for the 1988 season, which introduced a pre-qualifying system for the slowest entrants. Despite often being faster than some exempt cars, Tarquini repeatedly failed to pre-qualify, though his eighth place at the Canadian Grand Prix remains Coloni's best-ever Grand Prix result and his eight starts the most any Coloni driver ever achieved.
After briefly driving for the First team, Tarquini joined AGS midway through 1989 following Philippe Streiff's career-ending testing crash. He delivered strong performances including a threatening qualifying run at Monaco before running fourth in the race until an electrical failure. His best result came at the Mexican Grand Prix where he initially finished sixth, though he was classified outside the points after a successful appeal by Williams and Scuderia Italia over an earlier disqualification.
The AGS years proved increasingly difficult. Pre-qualifying became a gruelling elimination contest crowded with strong drivers in weak cars, and Tarquini alongside teammate Yannick Dalmas struggled to make the grid in the second half of 1989. The 1990 and 1991 seasons saw him qualify for only a handful of races as the team's financial position deteriorated severely. In late 1991 his contract was sold to Fondmetal, where he showed genuine speed including outqualifying Ivan Capelli's Ferrari in Belgium during 1992 before the team folded mid-season.
His final Formula One appearance came in 1995 as a Tyrrell test driver standing in for the injured Ukyo Katayama at the European Grand Prix, finishing 14th. He failed to pre-qualify on a record 25 occasions across his career, with 40 total failures to qualify overall — statistics that reflect the machinery rather than the driver, as many contemporaries regard Tarquini as a genuinely talented racer who spent his single-seater years in cars incapable of competing.
Tarquini's transition to touring cars unlocked his greatest success. He joined Alfa Romeo in the 1993 Italian Superturismo Championship, finishing third behind Roberto Ravaglia and Fabrizio Giovanardi. Moving to the British Touring Car Championship in 1994, he won the title at his first attempt, his Alfa Romeo featuring aerodynamic enhancements that drew considerable attention.
He remained in touring cars through various championships and manufacturers. In 2003 he won the European Touring Car Championship with Alfa Romeo via Nordauto, again at the first attempt. His peak achievement came in the World Touring Car Championship: after finishing runner-up to Yvan Muller in 2008 and 2010 while driving for SEAT Sport and its successor Sunred team, he claimed the 2009 WTCC title at the final round in Macau at the age of 47 years and 266 days, becoming the oldest FIA World Champion in history.
Tarquini returned to the front of the field in 2018, winning the World Touring Car Cup with BRC Hyundai at the age of 56, adding a fourth major touring car title to his record. He announced his retirement from racing at the 2021 Race of Italy. A 2005 Motor Sport magazine reader poll placed him 11th among the greatest touring car drivers of all time.
Following his retirement from driving, Tarquini became Sporting Director of Genesis Magma Racing ahead of the marque's entry into the FIA World Endurance Championship in 2026 with the Genesis GMR-001 chassis.