Born in Solotvyn, Galicia (part of Austria-Hungary) as one of the seven children of a vendor, he received a religious education in the local yeshiva (Jewish school), and spoke both Hebrew and Yiddish.
He became active in the Confédération Générale du Travail (CGT-F) and the Polish mission of the Main-d'œuvre étrangère (Foreign Workers Movement) to the Central Committee of the French Communist Party (PCF).
Feintuch, newly named Jérome, became the official supplier of paper and printing material to the Party's illegal press (which had been outlawed after the PCF had outraged public opinion and the Deladier government by condoning the Molotov–Ribbentrop Pact.)
When the German occupation of France began, Jérome was charged with maintaining contact with other elements of the Resistance, intellectuals as well as the Free French Forces of General Charles de Gaulle.
Some speculate that his activities brought the downfall of other communist Franc Tireurs Partisans (MOI), the group pictured in the Affiche Rouge led by Missak Manouchian.