Trenck entered the Imperial army in 1728 but resigned in disgrace three years later and decided to live peacefully in Požega, Slavonia. He married and lived on his estate for a few years. Upon the death of his wife who had perished in the black plague of 1737, he offered to raise an irregular corps of pandurs for service against the Turks, but this offer was refused, after which he entered the Imperial Russian Army as a mercenary. In Russia he met and befriended Ernst Gideon von Laudon. But after serving against the Turks and Tatars during the Russo-Turkish War for a short time as captain and major of cavalry he was accused of bad conduct, brutality and disobedience and condemned to death. Despite showing insubordination he had gained popularity for defying an order to retreat. His sentence was commuted by Field Marschal Münnich to degradation and imprisonment.