Oberndorff was born in Edingen-Neckarhausen, in the Grand Duchy of Baden, the son of Carl Gustav Adolph Maria Fortunatus Philipp Gabriel von Oberndorff, a landowner and count of the Holy Roman Empire, and his wife Marie Therese Henriette Franziska Eleonora Charlotte von Varicourt-Albini.
He passed the first state law examination in the spring of 1892 and graduated Doctor Iuris at Heidelberg on 9 August 1892.
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.
[1] 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 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.
Their daughter Liduina Maria Fortunata (born 1933) married Sir Peter Petrie, 5th Baronet, a British diplomat.