Ducarouge was born near Paray-le-Monial in Burgundy and trained in aeronautical engineering, earning a Baccalauréat Technique et Mathématique before completing his Degré Supérieur at the École Nationale Technique d'Aéronautique. He joined Nord Aviation in 1964, working on missile projects, before his restlessness led him to apply for a technician's position at Matra racing in December 1965 — shortly after the creation of Equipe Matra Sports.
At Matra he began on their Formula 3 programme, progressed to improving the Formula 2 cars, and steadily rose to head of operations. The pivotal design of his Matra years was the Matra MS80, powered by the Ford Cosworth DFV, which — entered by Ken Tyrrell's Matra International operation — won both the Drivers' Championship for Jackie Stewart and the Constructors' Championship in 1969. Ducarouge then designed the Matra MS670 sports prototype, which won the 24 Hours of Le Mans in 1972, 1973, and 1974 and delivered the World Championship for Makes to Matra in both 1973 and 1974 before the manufacturer withdrew from racing.
Following Matra's withdrawal, Ducarouge resigned to join Guy Ligier's newly formed Formula One team at Vichy, close to his home region. His first Ligier, the JS5, retained the Matra V12 engine and SEITA Gitanes sponsorship and debuted in 1976. At the 1977 Swedish Grand Prix the team scored its maiden victory, and Ligier went on to take further wins through the 1979 season.
In 1981 Ducarouge was fitting a revised Matra V12 into a new Ligier chassis with Talbot backing when Guy Ligier summarily dismissed him mid-season. He quickly moved to Alfa Romeo, where he persuaded the team to build their first carbon-fibre chassis — an innovation he had been eager to pursue. Despite this and other advances, Alfa Romeo failed to translate technical ambition into results, and after Andrea de Cesaris was disqualified at the 1983 French Grand Prix for his car being underweight, the blame fell on Ducarouge and he was dismissed again.
His period out of work was brief. Peter Warr of Team Lotus headhunted Ducarouge in 1983; the team had endured a prolonged downturn since their dominant 1978 campaign and the death of founder Colin Chapman in December 1982. Ducarouge joined following the Belgian Grand Prix and designed and built the Type 94T in five weeks, salvaging some success in the remaining rounds of 1983.
The revival he orchestrated at Lotus across 1984–87 represents the most celebrated chapter of his career. His 1984 Lotus 95T was widely considered the finest-handling chassis in the field; Elio de Angelis finished third in the Drivers' Championship, narrowly behind the dominant McLarens. For 1985 Ducarouge was joined by Ayrton Senna, and at a rain-soaked Estoril Senna drove the Lotus 97T to his maiden Formula One victory — the first of seven he would achieve in the car. His 1987 design, the Lotus 99T, was the first Formula One car fitted with a computer-controlled active suspension system and introduced the powerful Honda V6 turbo alongside that innovation.
When Senna moved to McLaren for 1988, Ducarouge developed the Lotus 100T using the same specification Honda turbo. Despite the engine parity, the car's aerodynamic data was reported to be compromised and the chassis insufficiently rigid, and Lotus failed to win a race for the first time since 1984 while McLaren swept fifteen victories.
Ducarouge left Lotus to join the Larrousse team, where he worked on the Lola chassis with Chris Murphy using Lamborghini V12 engines. Results were limited. In 1991 he returned to Ligier as Technical Director, remaining until mid-1994.
In the final phase of his career he returned to Matra as international development director, contributing to several projects including the Renault Espace F1 concept. Ducarouge died on 19 February 2015 at the age of 73. He left a body of work that included a world championship in each of the two eras he dominated — the DFV age of the late 1960s and the turbo age of the mid-1980s — making him one of the most consequential designers in French motorsport history.