In 1954-1963 he was Minister-President of Schleswig-Holstein. From 1955-1956, he was President of the German Bundesrat. He was closely associated with Ludwig Erhard's two Chancellorships, serving as Minister of Defense from 16 October 1963 to 1 December 1966. He then served in Kurt Georg Kiesinger's Chancellorship from 1 December 1966 to 21 October 1969 as "Minister of Displaced Persons, Refugees, and War Victims".
Following this ministership, he became president of the Bundestag from 5 February 1969 to 13 December 1972, after the previous president (Eugen Gerstenmaier) resigned amidst a financial scandal. He died aged 84 during the Charlemagne Award ceremony in the Aachen city hall in 1997.