born in viesly, depreux moved with his family to sceaux, hauts-de-seine in 1913. a soldier in world war i, depreux was injured in a gas attack, and was subsequently awarded the croix de guerre. he joined the section française de l'internationale ouvrière (sfio) at age 20, being influenced by the ideas of jean jaurès and jean longuet; he studied philosophy, law, and humanities, before becoming a lawyer.