During the Herzegovinian Uprising in 1875, Kosta Protić was sent by the Serbian government to Russia to investigate the possibilities for a war loan.

Ivan Aksakov received Protić, instructed him and gave him letters of recommendation to the right persons in Saint Petersburg; moreover, since Aksakov's wife was a former lady-in-waiting with connections at the court, she introduced Protić to the empress Maria Alexandrovna and to the heir, the future Alexander III of Russia.

The two were in favor of helping the Serbs of Bosnia and Herzegovina rid themselves of the Turks, more so than their government.

He served as the Chief of the Serbian General Staff during the Russo-Turkish War.

Upon the abdication of King Milan, Protić was appointed to a Regency council with Jovan Ristić and Jovan Belimarković for the underage Alexander I, on which he served until his death.