On 17 January 1701 Frederick Louis received the Order of the Black Eagle from the new King Frederick I of Prussia and shortly afterward was named Statthalter of East Prussia and Governor of Königsberg. During the War of the Spanish Succession, he participated in the Battle of Oudenarde in 1708, the Battle of Malplaquet in 1709, and the sieges of Lille, Mons, and Tournai. Frederick Louis was promoted to field marshal in 1713. The duke also secured neutrality for East Prussia during much of the Great Northern War. He died in Königsberg and was buried alongside his wife in Königsberg Cathedral.