Quidde joined the German Peace Society in 1892 (chairman 1914-1929), and in 1894 he founded a peace association in Munich. He was a prominent advocate of peace and pacifism. From 1907 to 1919 Quidde was a liberal member of the Bavarian parliament and member of the Inter-Parliamentary Union. In 1919 he joined the Democratic Party and from 1919 to 1920 he served as a member of the National Assembly. He denounced the German war-guilt clause of the Versailles Treaty and he opposed the revival of German militarism. He was chairman of the German Peace Cartel 1921-29. Quidde advocated German admittance to the League of Nations.