Served as Oberpräsident of Western Prussia from 1902 to 1905 and as that province's trade minister from 1905 to 1909. He simultaneously served as German Minister of the Interior and Vice-Chancellor from 1909 to 1916, when he was replaced by Karl Helfferich. After the war, he was one of the founding members of the German National People's Party (Deutschnationalen Volkspartei) and was a member of the Weimar National Assembly. Delbrück died on 17 December 1921 in Jena.