Milev was born in Mokreni (today Variko, Florina regional unit, Greece), a Bulgarian-populated village in Macedonia, then in the Ottoman Empire.

He finished the Bulgarian primary school in his birthplace and went with his father to Cairo, Egypt, where he lived for a period.

With the recommendations of Professor Vasil Zlatarski and with a Marin Drinov scholarship, Milev specialized history in Vienna, Florence and Rome from 1910 to 1912.

As President of the Association of the Journalists in Sofia, he protected the freedom of speech and press and, as grandmaster of the Zora freemason's lodge, he advocated for the cause of the Macedonian Bulgarians and an autonomous Macedonia.

Nikola Milev was considered among the potential foreign ministers of the new government after the Bulgarian coup d'état of 1923, but was rejected for of fear of the reaction of the State of Slovenes, Croats and Serbs and Greece.

The decision to murder Milev was approved by Stanke Dimitrov and the Central Committee of the Bulgarian Communist Party.

He had a chosen place among the elite of Bulgarian intellectuals that was difficult to fill again.”[4] Nikola Milev became one of the founders of the Macedonian Scientific Institute in 1923 and was elected to its first Board of Directors.

His monography of 1914 Catholic Propaganda in Bulgaria in the 18th Century is highly appreciated and it paved the way to his career of a university professor.