He succeeded his father, Duke Ernest I, in 1844. In 1852 he gave Gotha a new constitution, which in part coordinated the administration of his two duchies. In 1861 Ernest concluded a military agreement with Prussia. About this time he became patron of the Nationalverein (German: “National Union”) and allowed his court to become the centre of nationalist agitation. During the Seven Weeks' War of 1866, after vainly trying to mediate between Prussia and Austria, he put his troops under Prussian direction. His role in politics outside his own duchies ended when the German empire was formed. Because Ernest had no children, his title was inherited by his nephew Alfred, Duke of Edinburgh.