Rosier finished fourth at Silverstone in a Talbot in October 1948, competing in the RAC International Grand Prix — the first grand prix held in England since 1927. At the 1949 British Grand Prix at Silverstone, he drove a 4.5-litre unsupercharged Talbot-Lago to third place, one lap behind the winner, at an average speed of 76.21 mph. In June 1949 he won an International Grand Prix at Spa-Francorchamps, leading a 500-kilometre, 32-lap event from lap 23 to finish ahead of Luigi Villoresi in a time of 3 hours, 15 minutes, and 17 seconds.
Rosier debuted in the Formula One World Championship on 13 May 1950, ultimately contesting 38 World Championship Grands Prix and scoring two podiums for a total of 18 championship points. In 1950, driving for Talbot, he achieved back-to-back podium finishes at the Swiss and Belgian Grands Prix. He also won the Dutch Grand Prix in 1950 and repeated that win in 1951. In May 1953 he won the Grand Prix d'Albi driving a Ferrari, completing the 18-lap final at an average of 160 km/h. He placed second in a Ferrari at a Grand Prix in Aix-Les-Bains in July 1953. In April 1956, Rosier finished fourth at Aintree in a Maserati behind race winner Stirling Moss. He finished fifth at the 1956 German Grand Prix in a Maserati.
In 2016, an academic paper using mathematical modelling to assess the relative influence of driver and machine ranked Rosier as the 19th best Formula One driver of all time.
Rosier competed in nine editions of the 24 Hours of Le Mans between 1938 and 1956. In the 1950 race, run in a blue Talbot, his son Jean-Louis Rosier drove only two laps, meaning Louis effectively completed the race alone. The Rosiers covered 256 laps — 2,163 miles — in 23 hours, 54 minutes, and 2.2 seconds, finishing one lap ahead of Pierre Meyrat, who drove a car of the same marque.
Rosier owned and managed his own racing operation, Écurie Rosier. Originally set up to run his Talbot-Lago T26, the team evolved to run Maserati 250Fs and Ferrari 500s simultaneously for Rosier and a second driver. Throughout the 1950s, Écurie Rosier provided Formula One drives for Henri Louveau, Georges Grignard, Louis Chiron, Maurice Trintignant, André Simon, and Robert Manzon.
Rosier was a key sponsor of a proposed race circuit near Clermont-Ferrand. After World War II, Jean Auchatraire — president of the racing section of the local Automobile Club — and Rosier promoted the idea of a purpose-built circuit on the hilly landscape just outside the city. Preliminary designs called for a length of 4–6 km meeting contemporary safety regulations. The project was halted following the Le Mans disaster of 11 June 1955, which killed 84 people and led to a moratorium on racing on temporary urban tracks. Rosier, Auchatraire, and Raymond Roche — manager of the Reims-Gueux track — continued to seek political and financial support, but Rosier did not live to see the circuit open. The track was inaugurated on 27 July 1958 and named the Circuit de Charade Louis Rosier.
In 1951, Rosier designed a prototype based on the 4CV Renault. In 1953, working with Italian coachbuilder Rocco Motto, he developed a cabriolet using the barchetta concept he had raced at Le Mans, still built on 4CV Renault subassemblies. Approximately 200 units were produced by Brissonneau, and the model was shown at a car exhibition in New York. Rosier subsequently designed a roadster using Renault Frégate elements with an aluminium body by Motto on a multi-tubular frame; the revised engine and lightened body produced a car weighing 950 kg with 80 hp.
On 7 October 1956, Rosier was competing in the Coupe du Salon sports car race at Montlhéry driving a Ferrari 750 Monza when he crashed and sustained head injuries. He died three weeks later, on 29 October 1956.
This article is based solely on the supplied corpus. No external sources were consulted; claims that could not be substantiated against the corpus were omitted under the drop-the-claim rule.
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