Vonsyatsky embarked upon a military career in the Imperial Russian Army during the reign of Nicholas II. After the revolutionary events of October 1917, which brought the Leninist Bolsheviks to power and climaxed in the protracted Russian Civil War of 1917-1923, Vonsyatsky, newly admitted to St. Petersburg as a military cadet, took part in the anti-Bolshevik opposition and served in the counter-revolutionary White movement, first seeing action against the Red Army at Rostov. Leaving the White Army's stronghold in the Crimean Peninsula with the departing forces of General Wrangel, he was evacuated to western Europe in 1920.