He began his activist involvement with the Young Christian Workers ("Jeunesse Ouvrière Chrétien") in 1936. He became a militant of the French Resistance in 1940 and was one of the founders of the Movement of Young Christian Fighters ("Mouvement des Jenues Chretiens Combattants") in 1943. The movement was later fused with the Movement of the United Resistants ("Mouvement des Unies Résistents") to become the New French Youth ("Nouvelle Jeunesse Francaise") of which he was the secretary-general. This movement was one of many underground networks under the organization the United Forces of the Patriotic Youth ("Forces Unies de la Jeunesse Patriotique") that organized actions to inform the population, espionage to retrieve information, and sabotage or organization of military operations against the Axis powers. In 1944 he was captured and imprisoned in Fresnes by the Gestapo but escaped from the train transferring him to Mauthausen. He returned to Paris under a fake identity and became a militant activist participant in the Liberation of Paris of 1944.