Descended from a Swiss-German grandfather, Reutemann was the first successful Argentine Formula One driver to emerge since Juan Manuel Fangio's retirement in 1958. He began racing in 1965 in a Fiat saloon and progressed through Argentine touring cars and Formula 2 before moving to Europe in 1970 to drive in the European Formula 2 series. He drew attention at his first race at Hockenheim when he inadvertently eliminated Jochen Rindt on lap one, then recovered to finish fourth. The following season he finished a close second in the Formula 2 standings to Ronnie Peterson.
Bernie Ecclestone signed Reutemann for Brabham alongside Graham Hill for 1972. At his very first Grand Prix, in Buenos Aires in front of his home crowd, Reutemann qualified his Brabham BT34 on pole position — a feat previously only managed by Mario Andretti at a debut. He finished seventh after pitting to replace worn tyres.
In 1974, with the Gordon Murray-designed BT44, Reutemann took the first three victories of his Formula One career: in South Africa, Austria, and the United States. A fourth win was cruelly denied at the Argentine round when his car ran out of fuel while leading with less than two laps to go. He finished sixth in the championship. The following year, five podiums including a win at the old 14-mile Nürburgring allowed him to place third overall — his first of three third-place championship finishes.
In 1976, Brabham struggled with a new Alfa Romeo flat-12 engine plagued by reliability problems. After seven retirements in the first twelve races, Reutemann negotiated an early release from his contract and signed with Ferrari as a stand-in for the injured Niki Lauda. Lauda's unexpected recovery meant Reutemann raced only once for the team — at Monza in a third car.
Ferrari kept Reutemann for 1977 in place of the departing Clay Regazzoni. In the season's first two races, Reutemann finished third in Argentina and then won in Brazil, outperforming Lauda on both occasions and momentarily leading the championship. He later described his Brazilian victory as his best race. Over the full season, however, Lauda reasserted himself as team leader, eventually winning his second championship while Reutemann finished fourth.
When Lauda left for Brabham in 1978, Reutemann became Ferrari's senior driver alongside the young Gilles Villeneuve. He delivered his most productive Formula One season: four victories in Brazil, Britain, Long Beach, and Watkins Glen, plus a third-place finish in the championship behind Mario Andretti and the late Ronnie Peterson. At Brands Hatch, his win was particularly memorable — he passed a beleaguered Lauda for the lead at Clearways after Lauda was held up by a backmarker.
With a vacancy at Lotus following Peterson's death, Reutemann moved from Ferrari. The timing was poor: Lotus struggled while Ferrari, with the new 312T4, dominated and gave Scheckter and Villeneuve a 1–2 championship result. Reutemann managed only four podiums and finished seventh overall.
Joining Williams for 1980 put him back in competitive machinery. He won at Monaco and scored eight podiums across the season, finishing third in the championship. His partnership with world champion Alan Jones produced a Constructors' Championship-winning season for Williams.
The 1981 season brought Reutemann to the brink of the world title. He won in Brazil — disobeying a team order to let Jones pass — and in Belgium, accumulating enough points to arrive at the season finale in Las Vegas with a one-point lead over Nelson Piquet. Starting from pole, he fell backward through the field with early gearbox problems, losing fourth gear by lap two. He finished eighth, a lap down, and Piquet took the title by a single point.
Reutemann returned in 1982 but retired after just two races. The Falklands War had created severe political tensions between Argentina and Britain, and Reutemann chose to distance himself from the British Williams team. He was the last Argentine driver to win a Formula One Grand Prix.
After retiring from racing, Reutemann stood for election as Governor of Santa Fe and won, serving two terms (1991–1995 and 1999–2003). He went on to serve in the Argentine National Senate from 2003, representing the Justicialist Party. He was considered on multiple occasions as a potential presidential candidate but declined to seek the office. He died on 7 July 2021 in Santa Fe following complications from an intestinal haemorrhage, while still serving as a senator.
Reutemann also competed in rally events. He finished third in the 1980 Rally Argentina driving a Fiat 131, and returned to take another third place in the 1985 edition driving a Peugeot 205 T16 for Peugeot. He was, for three decades, the only Formula One driver to score championship points in both Formula One and the World Rally Championship.