In 1940, he was captured by the Germans as a French soldier. He managed to escape shortly thereafter. Poliakov joined the Résistance and participated in rescuing Jewish children. In 1943, working together with Isaac Schneersohn in the French Underground, he co-founded the Centre de Documentation Juive Contemporaine (CDJC, Centre for Contemporary Jewish Documentation), a historical commission to document the crimes against French Jews. Today, it is part of the Mémorial de la Shoah, the central Holocaust memorial site in France.