During the First Balkan War, the Third Army participated in the Battle of Kumanovo (23 - October 24, 1912) along with the Serbian First Army and the Serbian Second Army. It was composed of four infantry divisions and one infantry brigade (76,000 men), deployed in two groups, the first one at Toplica and the second one at Medveđa. It was assigned to the westernmost attack, with the task of taking Kosovo and then moving south to attack the left flank of the Ottoman Army.