Following the April 1941 Axis occupation of Yugoslavia Končar took part in the anti-fascist uprising which retook areas from German control in Serbia, and personally led attacks against Axis forces in Independent State of Croatia. Having relocated to Governorate of Dalmatia in October 1941, in November 1941 he was ambushed by fascist agents, arrested and beaten. The Ustaše disclosed his identity to Italian authorities who then put him on trial. Končar was sentenced to death and executed alongside twenty-five others on 22 May 1942 in Šibenik.