Grosjean was born on 25 July 1920, in Chalon-sur-Saône, France. He entered the French Air Force in 1939 and spent the next three years in various postings, among them Fighter Group (GC) 2/1 in Le Luc, Var. When the Germans invaded the non-occupied part of France in November 1942, Grosjean was demobilized. In the summer of 1975, at the height of his career, and while working on his new museum in Sartène, Grosjean died of a heart attack. He was fifty-five years old.