Siffert was born in 1936 in Fribourg, Switzerland, to a poor family — his father operated a dairy. At age 12, he attended the 1948 Swiss Grand Prix at the Bremgarten circuit with his father, and later cited that event as the moment he decided to become a racing driver. He initially made his name on two wheels, winning the Swiss 350 cc motorcycle championship in 1959, before switching to four-wheel competition with a Formula Junior Stanguellini.
Siffert entered Formula One as a privateer in 1962 with a four-cylinder Lotus-Climax. He moved through Scuderia Filipinetti before joining the private Rob Walker Racing Team in 1964 — the most successful privateer operation in the sport's history. Early non-championship victories in the 1964 and 1965 Mediterranean Grands Prix, both times defeating Jim Clark by very narrow margins, established his credentials.
His most celebrated Formula One moment came at the 1968 British Grand Prix at Brands Hatch, where he drove Rob Walker's Lotus 49B to victory over Chris Amon's Ferrari after a race-long battle. The win is regarded as the last genuine privateer victory in Formula One — a defining achievement for both Siffert and Walker. In 1971, driving for the BRM works team, Siffert scored his second World Championship victory at the Austrian Grand Prix at the Österreichring.
While Siffert's Formula One profile grew slowly, his reputation in sports car racing became formidable. He became a leading driver for Porsche's factory effort in its campaign for the World Sportscar Championship and was central to some of the manufacturer's most significant early victories. In 1968, partnered with Hans Herrmann in a Porsche 907, Siffert won both the 24 Hours of Daytona and the 12 Hours of Sebring — the first major outright wins in history for the company away from twisty circuit events. He followed these with multiple victories in major European rounds, including the 1000 km of Nürburgring, 1000 km of Spa-Francorchamps, and 1000 km of Zeltweg across 1968 and 1969.
In 1970, Siffert and Brian Redman won the Targa Florio in a Porsche 908/3. Porsche valued Siffert so highly that in 1970 they funded his seat in a works March Formula One entry rather than risk losing him to Ferrari. In 1971, he joined Pedro Rodriguez at BRM.
Siffert was killed at the non-championship World Championship Victory Race at Brands Hatch on 24 October 1971 — the same circuit where he had scored his first Formula One victory three years earlier. On the opening lap, contact with Ronnie Peterson damaged the suspension of Siffert's BRM. The damage caused the suspension to fail later in the race. The car crashed and immediately caught fire, and Siffert could not free himself. Three fire extinguishers at the scene failed to function properly, preventing rescuers from reaching him for five minutes. BRM did not acknowledge the suspension failure until it was accidentally revealed years later by a former mechanic.
The subsequent Royal Automobile Club investigation found that Siffert had suffered only a leg fracture in the initial impact and would likely have survived had the extinguishers worked correctly. He died of smoke inhalation. The accident directly led to mandatory on-board fire extinguishers using BCF (bromochlorodifluoromethane, an aviation product) and piped air into drivers' helmets — safety requirements that remained in place for many years.
Siffert's funeral in Fribourg was attended by an estimated 50,000 people. A Gulf-Porsche 917 from Team John Wyer led the hearse through the streets of his home city.
Siffert's 1968 British Grand Prix victory as a privateer stands as the closing chapter of an era in which independent teams could genuinely compete with works outfits at the highest level. His Porsche sports car record was exceptional: multiple wins across Daytona, Sebring, Spa, the Nürburgring, and Monza made him one of the defining sports car drivers of the late 1960s. The safety rule changes triggered by his death at Brands Hatch gave his loss a legacy that extended beyond his racing achievements.