Bell grew up near Pagham Harbour and was encouraged to take up racing by his stepfather, Bernard Hender. He started with a Lotus Seven in 1964, winning his first race at Goodwood, and progressed rapidly through Formula Three and Formula Two. Impressive performances in a privateer Brabham BT23C caught Enzo Ferrari's attention, earning him his Formula One debut for Ferrari at Monza in 1968.
His Formula One career with Ferrari, Wheatcroft Racing, McLaren, Surtees, and Tecno produced a best championship finish of sixth place at the 1970 United States Grand Prix in a Surtees TS7. Bell also competed in the 1969 Tasman Series and drove the experimental four-wheel-drive McLaren M9A at the 1969 British Grand Prix. Finding single-seater racing less fulfilling than sportscar competition, he progressively shifted his focus toward endurance racing, where his talent would define his career.
Bell's five Le Mans victories span an extraordinary period from 1975 to 1987. His first win came in 1975 partnered with Jacky Ickx in the Gulf Mirage GR8. The two drivers reunited in 1981 driving a Porsche 936 and again in 1982 in the Rothmans Porsche 956. His final two victories in 1986 and 1987 came alongside Hans-Joachim Stuck and Al Holbert in the Rothmans Porsche 962.
Bell's Le Mans involvement spanned from 1970, when he drove a works Ferrari 512 co-piloted by Ronnie Peterson, through to 1996, when he raced a McLaren F1 GTR. At the 1971 Le Mans test day, he reached a calculated top speed of 246 mph on the Mulsanne Straight in the JW Gulf Porsche 917LH — the highest speed of his Le Mans career. Bell considers finishing third with his son Justin at the 1995 Le Mans on Father's Day, in the Harrods-sponsored McLaren F1 GTR, among his proudest racing moments.
Bell's sportscar record extends well beyond Le Mans. He won the World Sportscar Championship title in 1985 and 1986, and the 24 Hours of Daytona three times in 1986, 1987, and 1989. In 1984 he won the Nürburgring 1000 km with Stefan Bellof in a Porsche 956, and claimed the 1973 Silverstone RAC Tourist Trophy with Harald Ertl in a BMW 3.0CSL.
His Spa 1000 km record is also notable: victories came in 1974 with Mike Hailwood in a Mirage M6, in 1975 with Henri Pescarolo in the Alfa Romeo Tipo 33TT12, and in 1984 with Bellof in the Porsche 956. This made Bell one of only two drivers to win the Spa 1000 km on both the original and current circuits, alongside Jacky Ickx.
During the filming of the 1970 Steve McQueen film Le Mans, Bell drove for the production and became close friends with McQueen. He narrowly escaped injury when a Ferrari 512 he was driving caught fire before a take.
After retiring from front-line competition, Bell became an ambassador for Bentley and consulted on the Bentley Speed 8 programme that won Le Mans in 2003. He has worked as an after-dinner speaker and motorsport commentator, and continues to participate in historic racing events. He returned to Le Mans in 2012 to race a Porsche 962 in the Group C support race.
Bell's son Justin followed him into motorsport; the two competed together at the 1991 Daytona 24 Hours and the 1992 Le Mans. Bell was the grand marshal at the 2014 Silverstone 6 Hours and the 2021 24 Hours of Le Mans.
Bell received the MBE in 1986 for services to motorsport. He won the BRDC Gold Star four consecutive times from 1984 to 1987, the Royal Automobile Club Plaque d'Honneur in 1985, and the Guild of Motoring Writers Driver of the Year award in 1982 and 1985. He was inducted into the Motorsports Hall of Fame of America in 2012 and the Le Mans 24 Hours Drivers Hall of Fame in 2013, and into the Motor Sport Hall of Fame UK in 2016. Hans-Joachim Stuck, one of his long-time co-drivers and rivals, has described Bell as one of the most liked drivers of his generation.