As an Imperial Russian general officer, Chernyshev commanded soldiers in the Seven Years' War. In 1757, he was at the Battle of Kolín, and in 1758, he joined forces with the Austrian army. For his leadership in the 1758 Battle of Zorndorf and the 1760 occupation of Berlin—capital of the Kingdom of Prussia, Chernyshev was awarded the Order of Saint Alexander Nevsky. In early 1762, then-General Chernyshev commanded a Russian corps of 16,000 infantry in Silesia that was attached to the Austrian army, fighting the Prussian kingdom. With the 1762 Treaty of Saint Petersburg, Peter III withdrew from the war and instead threw Russia's lot in with Prussia. Chernyshev was given command of the Russian forces now attached to the Prussian Army, and the Prussian monarch (Frederick the Great) awarded him the Order of the Black Eagle. When Emperor Peter III was replaced by Empress Catherine II later that year on 28 June, one of her first orders was to Chernyshev: immediately return to Russia with his corps, and if King Frederick interfered, "join the nearest army corps of her Imperial Roman Majesty, the empress of Austria ." Upon this change in alliances, Catherine II awarded Chernyshev with the Order of St. Andrew.