On 6 March 1813 Knesebeck was promoted to Colonel and Aide-de-camp to the king, becoming his closest military advisor. He was Prussia's main negotiator at the Treaty of Kalisch, which made its entry in the war on the side of Russia official and established Prussia's post war borders. This agreement was broadly adhered to at the later Congress of Vienna. He was subsequently sent to Vienna to prepare Austria's participation in the War of the Sixth Coalition. In the same year he was promoted to Major-General. He spent most of the conflict in the Coalition headquarters, participating in the costly battles of Lützen and the Bautzen, where he directed the army's orderly retreat. He was thereafter a driving force behind the Truce of Pläswitz, which allowed the Coalition time to consolidate its forces for the upcoming campaign.