Born in Roskilde, Magnussen showed exceptional single-seater talent from an early age. He won the 1992 Formula Ford Festival at Brands Hatch before dominating the 1994 British Formula 3 Championship with Paul Stewart Racing, winning fourteen of the eighteen events and breaking Ayrton Senna's F3 record. That extraordinary season earned him comparisons to the all-time greats: team founder Jackie Stewart described him as "the most talented young driver to emerge since Ayrton Senna."
Magnussen made his Formula One debut at the 1995 Pacific Grand Prix at Aida, stepping in for an unwell Mika Häkkinen and becoming the first Danish driver to compete in F1 since Tom Belsø in 1974. For 1997 and 1998 he held a full seat at the newly founded Stewart Grand Prix team, but his performances failed to match the enormous expectations that surrounded him. He scored a solitary championship point at the 1998 Canadian Grand Prix — his last F1 race — before being replaced mid-season by Jos Verstappen. Over 24 starts he was unable to translate his junior-formula brilliance to the top tier.
After leaving Formula One, Magnussen moved into American sports car racing, competing in the American Le Mans Series from 1999 onwards, initially with Panoz. The switch proved transformative. In 2001 he joined Corvette Racing and found the environment and machinery to match his talents. The Chevrolet Corvette program, run under the General Motors factory banner, would become his professional home for two decades.
Magnussen competed at the 24 Hours of Le Mans every year from 1999 onward, accumulating a remarkable record in the GT classes. His four class victories at Le Mans came in 2004 (GTS class), 2005 (GT1 class), 2006 (GT1 class), and 2009 (GT1 class). The 2005 and 2006 victories were shared with Oliver Gavin and Olivier Beretta; the 2009 triumph partnered him with Johnny O'Connell and Antonio García.
Beyond Le Mans, Magnussen built an equally impressive record at other major endurance events. He won the GT1 class at the 12 Hours of Sebring in 2006, 2008, and 2009, and claimed the GT1 class at the 2015 24 Hours of Daytona in the GTLM category. He won the GT1 class in the American Le Mans Series in 2008 and took the GT Drivers Championship in 2013, both with Corvette Racing.
At the broader championship level, Magnussen won the IMSA SportsCar Championship twice, in 2017 and 2018, partnering Antonio García in the Chevrolet Corvette C7.R in the GTLM class.
Throughout his sports car career Magnussen maintained an active programme in Danish and Scandinavian touring cars. He drove in the Danish Touring Car Championship (DTC) between 2001 and 2010, taking the title in 2003 and 2008. He piloted various machinery there including Peugeot, Chevrolet Lacetti, and Toyota Corolla variants.
In 2010 he made a one-off NASCAR Sprint Cup appearance at Infineon Raceway, driving the No. 09 HendrickCars.com Chevrolet for Phoenix Racing and finishing twelfth from a thirty-second grid position. That same year he competed in the GRAND-AM Rolex Sports Car Series with Stevenson Motorsports.
Magnussen continued as a Corvette Racing factory driver until the end of the 2020 season, an association that lasted nearly two decades. During that span he competed at Le Mans continuously across multiple decades, a feat that places him among the most enduring presences in international endurance racing. In 2023 he won the Aurum 1006 km endurance race in Lithuania driving a Mercedes-Benz AMG GT3 Evo.
His son Kevin Magnussen followed him into motorsport and competed in Formula One with Haas, McLaren, and Renault before joining the FIA World Endurance Championship and IMSA with BMW. Magnussen's nephew Dennis Lind and youngest son Luca are also racing drivers, making the family a notable multi-generational presence in motorsport.
Jan Magnussen's career represents one of the most striking pivots in modern racing history — a driver whose single-seater trajectory stalled at the highest level but who found sustained excellence and multiple major victories over two decades in GT endurance competition.