Vasily Fedorovich (Willim Ferdinandovich) Mertens was born on March 8 (19), 1761, in a family of Prussian immigrants. His father, Friedrich Khristoforovich, was a field officer in the Russian army. Vasily Mertens began his service in 1773 as a soldier in the Dinaburg Border Battalion. Then, he was a non-commissioned officer in the Preobrazhensky and Life-Guard Horse regiments. From 1784, he used to be a lieutenant of the Chevalier Guard Corps, from 1790 - the captain of the Yelets Infantry Regiment. Vasily Mertens participated in the Russian-Swedish war of 1788–1790. He resigned in 1790. In 1800, he was appointed vice-governor of Perm, and then - the governor of Tver Province.