In December 1895, Oberndorff was admitted to the Imperial foreign service, and after a period of training joined the active diplomatic service of the
German Empire in February 1897. In 1905 he was posted as first secretary in
Brussels and in 1907 returned to Madrid, with the rank of Counsellor. In 1910 he was posted to Vienna. Two years later, he got his first posting as a head of mission, serving from 1912 to 1916 as Envoy Extraordinary and Minister Plenipotentiary at the Royal Norwegian Court in
Kristiania, where he was when the First World War broke out. From 1916 to 1918 he headed the German mission in
Sofia,
Bulgaria, a significant promotion, as Bulgaria was one of the
Central Powers and a German war ally. Oberndorff next returned to the Foreign Ministry in Berlin as head of foreign policy. In that capacity, he attended the negotiations for the Armistice of Compiègne, with
Matthias Erzberger, who was
minister without portfolio, Major General
Detlof von Winterfeldt, representative of the
Supreme Army Command to the
Chancellor of Germany, Captain Ernst Vanselow, of the
Imperial German Navy, and two translators. On 11 November 1918, the four men were the German signatories to the Armistice. In 1920 and 1921 Oberndorff was the first German
chargé d'affaires in
Warsaw after the
Second Polish Republic had emerged as an independent state from the ruins of the
Russian Empire. He was recalled to Berlin in February 1921. Oberndorff was a founding member of the Franco-German Study Commission, which in the 1920s advocated
rapprochement between Germany and France. He continued to serve in the foreign ministry of the
Weimar Republic and remained there for a few months after the rise to power of
Adolf Hitler. He retired in July 1933, after the
Enabling Act of 1933 and the
Night of the Long Knives. Oberndorff died in
Heidelberg in March 1963 and is buried in the family plot in
Neckarhausen. ==Personal life and descendants==