Vojinović was born in Smederevo, Kingdom of Serbia, to parents who had fled from the Vučitrn area in Kosovo, due to Albanian zulum (exploitation, oppression, wrongdoing), the region at the time being part of the Ottoman Empire.

[1] He came from a respected family, his father Jovan having finished military school in Russia and upon returning to Serbia he worked as a state clerk of the general tax administration, and later was the president of a municipality in Kosovska Mitrovica up until World War I.

[1] His day-to-day traveling work gave him time to undetectably enter Serb villages and contact Chetniks from whom he received information on battles and successes.

[1] In September 1915, when the Central Powers with full force broke down Serbia, wearied by previous battles and epidemic typhus fever, Kosta Vojinović found himself in the renewed detachment of Vojvoda Vuk which was forwarded to the Čemernik mountain towards Bulgaria, to provide security for the Serbian Armies.

[1] There, he was taken in and promised (besa) by Albanian Ali Šalja, who illegally transferred him to his father, who had up until the occupation worked as a president of the municipality of Kosovska Mitrovica.