In 1919, in the Black Sea when he was with the French Navy, Thắng claimed to participate in a plot with fellow sailors to turn over the French armored cruiser "Waldeck-Rousseau" to the enemy Bolshevik revolutionaries. He continued to participate in rebellious activities against the French, was member of Vietnamese Revolutionary Youth Association since 1927; and in 1929, he was imprisoned by the French at Sai Gon, deported to Côn Sơn Prison. He remained there until 1945 and immediately rose again into the public eye. After Hồ Chí Minh’s Viet Minh came into power in August 1945, Thắng became the member Cochinchina Party Committee of CPV, member Administration Resistance Committee of Cochinchina and since 1946, the presiding member of the National Assembly. In 1947, he became a member of the Central Committee of the Communist Party of Vietnam.