Leontiev was born on 25 February 1862 to a noble family in Kherson Province. He studied in Nikolaev's Cavalry military school, then served in the UhlanLeib Guard regiment. In 1891, he became esaul of a military reserve force of the Umansk regiment of the Kuban Cossack army. Like Mashkov and Ashinov before him, Leontiev had dreamed of going to Ethiopia and for many years he collected information about the country. Finally, Leontiev was able to go to Ethiopia on a research trip. Famous scientists, the Science Academy and the Russian Geographical Society took great interest in this programme. But the main task of the Leontiev expedition was to establish friendly relations between Russia and Ethiopia. Leontiev was the chief of the eleven-man Russian expedition; stabskapitan Zviagin was his deputy. The meeting between Leontiev and the Ethiopian emperor Menelik II set up the foundation for their mutual friendship. When Leontiev decided to go home, Menelik sent his first diplomatic mission to Russia with him, and in doing so abrogated an agreement with Italy that forbade such diplomatic missions.
Menelik invited Leontiev to return to Ethiopia with a Russian military mission. In 1895 Leontiev organized a delivery of Russian weapons for Ethiopia: 30,000 rifles, 5,000,000 cartridges, 5000 sabres, and a few cannons. The presence of the Russian advisers at the battle of Adwa helped the Ethiopians achieve victory in the first Italo-Ethiopian War. The Russian advisor Leonid Artamonov wrote that the Ethiopian artillery comprised 42 Russian mountain guns supported by a team of fifteen advisers. How writes in the book of Alexander Bulatovich during him courier's marathon for arrival to Ethiopia so phenomenal showy by reason of record speed with the use of camel, Leontiev meets him to give help. Leontiev returned to St. Petersburg, and then visited Italy and Turkey. In summer 1897, Count Abai was appointed governor-general of the Ethiopian equatorial provinces. In accordance with the order of emperor of Ethiopia, Directly Nikolay Leontiev organized one of military expeditions of the Ethiopian army to the region of Lake Rudolf. The Russian officers-volunteers participated in this expedition: Shedevr, Babichev, Agapov, Adzeiv, Petrov et cetera. A brigade had more 2000 Ethiopian soldiers, but cossacks there were most exotic of all. A brigade lost 216 persons as killed or injured, Shedevr was injured and the cossack Gogasov perished. Count Abai was able solemnly report to the emperor Menelik II, how the young romantic poruchik Shedevr solemnly heaved up the flag of Ethiopia above one of banks of Lake Rudolf. Emperor of Ethiopia introduced the title of count, which had never existed in his country before, Nicholai Leontyev was handed an official document that declared him to be Count Abai. Leontiev organized the first modern battalion of the regular Ethiopian army and presented it to Menelik in February 1899. Leontiev formed the first regular battalion, the kernel of which became the company of volunteers from the former Senegal shooters, which he chose and invited from Western Africa, with training of the Russian and French officers. The first Ethiopian military orchestra was organized at the same time. Leontiev was in Peking with the Russian contingent in 1900 during the Boxer Rebellion. A wound forced Leontiev to leave Ethiopia. Later, he took part in the Russo-Japanese War. Leontiev died in Paris in 1910, but his body is buried in Saint Petersburg.
