Stewart was born in Milton, Dunbartonshire, Scotland. His father had been an amateur motorcycle racer, and his brother Jimmy Stewart was a racing driver. Stewart attended Hartfield primary school and Dumbarton Academy, experiencing learning difficulties due to undiagnosed dyslexia. He began working in his father's garage as an apprentice mechanic and was not diagnosed with dyslexia until 1980.
At 13, Stewart won a clay pigeon shooting competition and became a prize-winning member of the Scottish shooting team. His first car was an Austin A30. In 1961, Barry Filer provided a Marcos, in which Stewart scored four wins. He also competed once in Filer's Aston DB4GT. In 1962, he tested a Jaguar E-type at Oulton Park, matching Roy Salvadori's times. David Murray of Ecurie Ecosse offered him a ride in the Tojeiro EE Mk2 and their Cooper T49, in which he won at Goodwood. For 1963, he earned fourteen wins.
In 1964, Stewart again signed with Ecurie Ecosse. Ken Tyrrell, running the Formula Junior team for the Cooper Car Company, offered Stewart a spot on the team after a tryout at Goodwood. Stewart drove in Formula Three for Tyrrell, winning the F3 championship. He then went to the Lotus Formula Two team, finishing second at Circuit Clermont-Ferrand in a Lotus 32-Cosworth.
Stewart signed with BRM alongside Graham Hill in 1965. His first race in an F1 car was for Lotus at the non-championship Rand Grand Prix in December 1964. On his World Championship F1 debut in South Africa, he finished sixth. He won his first World Championship race at Monza and finished his rookie season in third place in the World Drivers' Championship.
In 1966, Stewart won the Tasman Series from Graham Hill. In F1, he won the Monaco Grand Prix in a 2-litre engined car. He had an accident at the Belgian Grand Prix at Spa-Francorchamps, which sparked his campaign to improve safety in F1. He almost won the Indianapolis 500 on his first attempt, in John Mecom's Lola T90-Ford, only to be denied by a broken scavenge pump. Stewart won Rookie of the Year honors for his performance. In 1967, Stewart closely contested the Tasman Series with Jim Clark, winning a victory in the New Zealand Grand Prix.
For 1968, Stewart switched to Tyrrell's Matra International team, driving a Matra MS10-Cosworth. He won in heavy rain at Zandvoort and by four minutes at the Nürburgring. In 1969, driving the Matra MS80-Cosworth, Stewart won by over two laps at Montjuïc, a minute in front at Clermont-Ferrand, and by more than a lap at Silverstone. With additional wins, Stewart became world champion.
For 1970, Tyrrell decided to build his own car and bought a chassis from March Engineering. Stewart took the March 701-Cosworth to wins at the Daily Mail Race of Champions and Jarama. The new Tyrrell 001-Cosworth appeared in August. Stewart also had a one-off race in Can-Am in the Chaparral 2J.
Stewart won the F1 World Championship in 1971 using the Tyrrell 003-Cosworth, winning Spain, Monaco, France, Britain, Germany, and Canada. He also did a full season in Can-Am, driving a Carl Haas sponsored Lola T260-Chevrolet. During the 1972 season, he won the Argentine, French, U.S., and Canadian Grands Prix to come second to Emerson Fittipaldi in the drivers' standings. In 1972, Stewart also received the OBE.
Entering the 1973 season, Stewart had decided to retire. He won at South Africa, Belgium, Monaco, and the Netherlands. His last and then record-setting 27th victory came at the Nürburgring. After the fatal crash of his teammate François Cevert in practice for the 1973 United States Grand Prix at Watkins Glen, Stewart retired one race earlier than intended. Stewart had already won the Drivers' Championship at the Italian Grand Prix two races previously.
After his crash at Spa-Francorchamps in 1966, Stewart became an outspoken advocate for auto racing safety. He campaigned with Louis Stanley for improved emergency services and better safety barriers around race tracks. Stewart pressed for mandatory seat belt usage and full-face helmets for drivers. He also pressed track owners to modernize their tracks, including organizing driver boycotts of races at Spa-Francorchamps in 1969, the Nürburgring in 1970, and Zandvoort in 1972.
Stewart began a partnership with the Ford Motor Company in 1964 that lasted 25 years. He covered F1 races, NASCAR races, and Indy car races as a color commentator for ABC's Wide World of Sports and NBC Sportsworld. He was noted for his insightful analysis, Scottish accent, and rapid delivery. Stewart was often critical of driver safety in his broadcasts. He later worked on Australian, Canadian, and British TV coverage.
In 1997, Stewart returned to Formula One with Stewart Grand Prix, as a team owner in partnership with his son, Paul Stewart. The team's first race was the 1997 Australian Grand Prix. The team won one race at the European Grand Prix at the Nürburgring with Johnny Herbert. The team was later bought by Ford and became Jaguar Racing.
Nicknamed "The Flying Scot", Stewart received Sports Illustrated magazine's 1973 "Sportsman of the Year" award. In 1990, he was inducted into the International Motorsports Hall of Fame. In 2001, he received a knighthood for services to motor racing. Stewart has been married to Helen McGregor since 1962, and they have two sons: Paul and Mark. In 2014, Helen McGregor Stewart was diagnosed with frontotemporal dementia. In 2018, Stewart set up the charity Race Against Dementia.
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