A former motorcycle racer and hill-climb specialist, Rosier had just started to develop his racing career when the war intervened, and it was 1947 before this garage owner from Clermont Ferrand could compete on a wider stage. Equipped with his self-prepared Talbot, Rosier won the 1947 Albi GP after more speedy opponents had dropped out and this win obviously set the tone for the rest of his career, for he usually raced well within his limits and placed great store by strategy and reliability as a route to success. In 1948, as a member of the Ecurie France team, he took delivery of a single-seater Lago-Talbot, winning the Grand Prix du Salon and finishing fourth at the Comminges, Pau and British GPs. The following season, with the Talbot probably at its peak relative to the opposition, Rosier won the Belgian GP and, with a succession of steady finishes, was crowned champion of France, a title he was to hold for four years.