Hart was born in 1936 and came to motorsport from the aviation industry. He began racing in 1958 with a Lotus Seven in the 1172 championship. In 1959 he partnered with designer Len Terry, driving the Terrier Mk2 and winning the Chapman Trophy. He drove Terry's front-engined Formula Junior Terrier Mk4 in 1960, developing a downdraught head for the Ford Anglia engine used in the car. A serious crash at Oulton Park in October 1960 led Terry to redesign the car for the following season.
Hart went on to compete in Formula Junior and Formula Three, then moved up to Formula Two with the works Lotus team run by Ron Harris. He appeared in a handful of non-championship Formula One races with F2 machinery and in 1967 qualified for the German Grand Prix at the Nürburgring in a Protos-Cosworth. He retired from driving in 1971 as his engineering commitments increased.
Towards the end of 1967 Hart began working at the de Havilland aircraft company in Hatfield, where he received training in airframe and aero engine design. He then joined Cosworth, but left in 1969 to set up his own company to service Cosworth's Ford FVA engines. Brian Hart Limited was quickly commissioned by Ford for new engine development work. Hart developed the Ford BDA, which powered Ford's rally programmes throughout the 1970s.
Hart-tuned FVA and BDA engines proved competitive in Formula Two. Ronnie Peterson won the European F2 title in 1971 with an FVA-powered car, and Mike Hailwood repeated the achievement in 1972 with a BDA. When BMW and Renault entered F2 and Ford declined to increase its investment, Hart developed his own F2 engine, the 420R, first raced in a Chevron sports car in 1976. The engine won races in F2 in 1977 and 1978.
The Toleman F2 team committed finance to Brian Hart Limited's research and development in the 1978–79 off-season. Toleman-Hart dominated the 1980 European F2 Championship, with Brian Henton and Derek Warwick finishing first and second in the standings.
Hart developed a turbocharged version of the 420R for Toleman's entry into the Formula One World Championship in 1981. Although the engine was initially underpowered and unreliable, Toleman-Hart established themselves as a legitimate constructor, famously providing the car in which Ayrton Senna drove a celebrated wet-weather performance at the 1984 Monaco Grand Prix. Hart continued supplying Toleman until Benetton purchased the team, and in the 1980s also provided engines to RAM, Haas Lola, and Tyrrell.
After the ban on turbocharged engines at the end of 1988, Brian Hart Limited reverted to its roots as a tuning and development partner, working with Cosworth to develop the DFZ and DFR naturally aspirated V8 engines for the less well-funded teams.
By 1992, Hart had funded the design of his first V10 engine, the Type 1035, and announced an exclusive two-year deal to supply Jordan Grand Prix. The partnership produced notable results, including Rubens Barrichello's third place at the 1994 Pacific Grand Prix in Aida. When Peugeot offered Jordan a factory deal, Hart lost the contract and moved to supply Footwork/Arrows, whose financial difficulties prevented meaningful engine development.
In 1997, Hart began work with Minardi on a new V10 design. When Tom Walkinshaw purchased Brian Hart Limited through the Arrows organisation, the injection of capital allowed that design to become the Arrows V10, but the business relationship ended amid legal disputes over money owed, and Hart parted company with Arrows before the end of the year. Arrows itself went into liquidation in 2002.
Brian Hart Limited occupied an unusual and important position in Formula One as an independent British engine builder that competed — often with limited resources — against factory operations from Ferrari, Renault, and Honda. Hart's work underpinned the early careers of teams including Toleman and Jordan, and his developmental contributions to the Ford BDA and the Cosworth DFZ and DFR extended those engines' competitive lives well beyond their original design scope.