He mainly represented (also as a member of supervisory boards) firms in the steel and coal, potash and railway rolling stock businesses.

After Gustav Stresemann died on 3 October 1929, Curtius became the acting Foreign Minister and in November vacated his old position and took over the Auswärtiges Amt.

As the minister responsible for the Young Plan, Curtius was heavily criticized by DNVP, Der Stahlhelm, Nazis and the Pan-German League, who labelled him a "traitor to the fatherland".

However, France blocked this by putting economic pressure on Austria and by bringing about a decision by the Permanent Court of International Justice at The Hague, which voted 8:7 to rule the union in contradiction of the Geneva protocol of 1922 (see Anschlussverbot [de]).

After his house in Berlin was destroyed in World War II and his estate in Mecklenburg was seized by the Communist authorities he moved to Heidelberg in July 1946.