He served as ambassador in Belgrade, Brussels, Buenos Aires and Ankara, and represented Germany at the Geneva Disarmament Conference in 1933.

He was born in Munich, son of the later-ennobled Royal Bavarian Lieutenant General Eugen Keller [de] (1843–1938) and Berta Hassold (1846-1929).

[1][2] Keller studied law at the Würzburg University, worked for the Bavarian Ministry of Justice from 1895 in earned his doctorate in 1896.

After the end of World War I, he was considering to continue scientific work at the University of Würzburg, but was sent by the Foreign Office to the peace negotiations at Versailles.

[4] She was married to Guido Dessauer, a notable physicist and specialist in paper engineering, who commissioned Horst Janssen to produce a portrait of Keller.