 At the West German Foreign Office, he became acting head of the legal department (1953 – 1954), head of the Political Department (1955 – 1958), and from 1954 to 1955 he led the West German observer delegation at the Four Powers Conferences in Berlin and Geneva.Grewe played a major role in formulating the Hallstein Doctrine (1955- ).Grewe served as West Germany's ambassador to Washington (1958-1962) and to Tokyo (1971 – 1976) and he was Permanent Representative to the North Atlantic Council at NATO headquarters in Paris and Brussels (1962 – 1971).