Westarp had joined the German Agrarian League in the 1890s, his political advancement began in 1908 as a member of the German Reichstag parliament as a member of the German Conservative Party, from 1913 to 1918 as head of the parliamentary group. During World War I, he agitated against the 1917 Reichstag Peace Resolution, advocated the use of unrestricted submarine warfare and rejected the reform of the Prussian three-class franchise initiated by Chancellor Bethmann Hollweg.
