[1][2] At the outbreak of World War II in 1939, he was in a Chasseurs Alpins unit and volunteered for a Norwegian expedition in Narvik in the spring of 1940.
On his return from Narvik that year, he took part in fighting in Brittany before being evacuated to England on 18 June, just before the armistice with the Nazis.
He contacted local Confédération générale du travail and Confédération Française des Travailleurs Chrétiens trade unionists and then in Marseille, Clermont-Ferrand, Montluçon and Lyon, preparing the ground for the resistance leader Jean Moulin, whom he met in January 1942, in Valence.
As a member of the Libération steering committee, he identified parachuting grounds, had the idea of Le Bureau d'Information et de Presse (BIP) which was then instigated by Jean Moulin, and continued creating resistance network links before being recalled to London in November 1942, after being sentenced to death in absentia.
He worked with André Philip and then enlisted in the Free French Air Forces in May 1943, serving as a lieutenant in the 1er Bataillon d'infanterie de l'Air before being appointed as the youngest member of the Provisional Consultative Assembly of Algiers.
Continuing his previous liaisons, he became an assistant to Alexandre Parodi, the general delegate of the GPRF for the Resistance and French Committee of National Liberation, preparing with him the administrative measures to be put in place after the Allied landing.
During the Liberation of Paris, Morandat arrived on a bicycle with his wife at the Hôtel de Matignon and claimed it on behalf of the Provisional Government of France.
In 1947, he joined the Charbonnages de France (French coal board) as executive attaché and became head of the press service.