In 1936, due to activities of Popular Front, France, Cung was released from prison. He then continued participate in communist movement in Nha Trang and then in Nghe An. In early 1945, he was a co-founders of Viet Minh in Nghệ-Tĩnh. When August Revolution broke out, Cung was the secretary of Viet Minh Front in Nghệ-Tĩnh.