After the invasion and occupation of the Kingdom of Yugoslavia in 1941, he left his studies and joined the anti-fascist movement in Yugoslavia. He first worked politically in occupied Zemun and its surroundings where he took part in preparing and organizing sabotages and diversions against the occupying forces. He later joined the Yugoslav Partisans where he entered into Bosnia as a member of the Vojvodina Brigades. During the war he was a political commissar and battalion commander. He became a member of the Communist Party of Yugoslavia in 1942.