[2] He was forced to flee his home in 1767, after feuding with a local Turk and killing him; at Galaxeidi he managed to board a vessel that brought him to the island of Zakynthos, then still under Venetian rule.

He joined the infantry corps of Greek volunteers set up by the Russians, and distinguished himself due to his intelligence and resolve during the rest of the Russo-Turkish War of 1768–1774.

[2] When the Russo-Turkish War of 1787–1792 broke out, Katsonis went to Trieste, where with his own money, and through donations from the local Greek community, he bought and equipped a 24-gun warship, and began to raid Ottoman shipping.

[2] His 1789 campaign was even more successful: he gathered a fleet of 17 vessels with 500 guns, and captured Kea Island, which he fortified and made his base of operations.

[2] The Ottomans tried to entice him to their side, sending the Dragoman of the Fleet with a letter promising him amnesty for himself and his followers, a salary of 200,000 gold coins, and lordship over an island of his choice.

Taking on board the klepht chieftain Andreas Androutsos [el] and his 800 men, he raided Turkish shipping in the Aegean, advancing up to Tenedos, blocking the entrance to the Dardanelles and hoping to confront an Ottoman fleet.

[8] Despite his defeat, he was rewarded by Empress Catherine, on the recommendation of Grigory Potemkin, with promotion to Colonel and the Cross of St. George, 4th Class.

[10] In the meantime, however, the Russian victories at Măcin and Kaliakra led to the war's end with the conclusion of an armistice on 11 August 1791, followed by the Treaty of Jassy.