Darko was the youngest son of the renowned Slovene physician from Carniola, Franc Ribnikar and brother of Vladislav Ribnikar. He was educated in Svilajnac and Belgrade. He graduated in law in Germany (Berlin and Jena). After the death of his father, in 1905, he returned to Belgrade to assist his brother Vladislav with "Politika". He was editor in chief for the newspaper but also served as special correspondent in Romania during the Peasant revolt of 1907 and during the Friedjung process in Vienna in 1909.