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 he 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. 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. By 1951 the Talbot was no longer a competitive proposition. The 1952 season brought a change of regulations, and Rosier lost no time in getting his hands on a Ferrari T375 and a state-of-the-art Ferrari T500 F2 car. The Italian machines were naturally painted French blue, and Rosier quickly put one of them to good use, winning the Albi GP in the big-engined model. For 1953 he continued with the same equipment, taking yet another win in the Albi GP and a victory in the Sables d’Olonne GP with the T500.By now Rosier was well past his best as a driver, but he pushed ahead undaunted the following season, and after racing a Ferrari 625 he bought a Maserati 250F which he continued to campaign in Grand Prix and non-championship events in a steady and reliable fashion, as well as handling his own Ferrari 3-litre sports car. Ironically, Rosier shared a Maserati T300S with Behra to win the 1956 Paris 1000 Km, his last win, before returning to the Montlhéry circuit he knew so well in this Ferrari for the Coupe du Salon. In pouring rain, Rosier overturned his car and suffered severe head injuries from which he died three weeks later. He was posthumously awarded the French Order of the Nation.