[7] With the onset of the invasion of Yugoslavia in 1941 (also known as the April War), Todorović, now at the rank of lieutenant colonel, was sent to the area to assist resistance fighters, known collectively as the Chetniks.

He joined the Ravna Gora Movement, a resistance cell led by Dragoljub "Draža" Mihailović,[8] serving as a communications officer.

[16] In July 1941, upon expanding the influence of the Ravna Gora Movement cell, Mihajlović gave Todorović command of the northern province, based in Belgrade.

In this position, Todorović started with activities aimed to establish Chetnik undercover operations in German-occupied Belgrade.

[18][19] German officer Paul Bader boasted in the report he sent to his superior commander that the arrest of Todorović was a heavy loss for Mihajlović's organization in Belgrade.

[23] After Todorović was released he was used by Hans Helm, a German attache with the Croatian Ministry of Internal Affairs, to trace other members of his intelligence network.

[24] Todorović survived in Mauthausen for six months until the end of the war, managing to make a vegetable garden - the produce of which he shared with other inmates.