He joined a hussar regiment and, under Suvorov's command, took part in the Russo-Turkish War, 1787-1792, and the Polish Campaign of 1794-1795 inclusive of the Brześć and Praga (Warsaw) battles.

He encouraged guerrilla fighting and fought with distinction at Lapua, Kuortane, Oravais — three engagements which earned him Order of Saint George and the rank of Major General.

Kulnev also won a notable victory at Pyhäjoki in the early part of the war, but was defeated by a much larger Swedish force at Siikajoki.

Kulnev crowned the campaign by leading Bagration's vanguard across the frozen Baltic Sea towards the Åland Islands and thence to Grisslehamn, within 70 km from the Swedish capital, Stockholm.

Awarded for his courage with Order of Saint Anna of the 1st Degree, Kulnev was invited to take charge of the vanguard of the Danube Army which fought against the Turks in Bulgaria.

His bold leadership made itself felt at Shumla, Nikopol, Rousse, and Batin, giving the campaign a character of decision it had been lacking heretofore.

A typical Romantic hero of the Napoleonic Wars, he emancipated his serfs and was reputed to live in poverty, in order to emulate the soldiers of Roman antiquity that were his ideal.