After serving as a naval officer during World War I, he entered the Foreign Office in 1920 occupying various consular and diplomatic posts. From Consul in Basel (1922) and embassy Councillor in Copenhagen, he rose to the position of Minister in Oslo (1931-3) and Minister to Switzerland (1933-6). In 1937 he was appointed Ministerial Director and, following von Ribbentrop’s nomination as Foreign Secretary, he became Chief State Secretary in the Foreign Office in Berlin, a post he held until 1943.
For the last two years of the war, the compliant von Weiszacker was German Ambassador to the Vatican. Arrested and placed on trial as a war criminal by the Allies, von Weiszacker was sentenced on 2 April 1949 to five years’ imprisonment by an American military tribunal at Nuremberg.
Eighteen months after his conviction he was released under a general amnesty. In 1950 von Weiszacker published his self-justificatory memoirs.
An old guard diplomat, von Weiszacker doubtless viewed the permeation of the Foreign Office by Nazis with some distaste, but this never prevented him from initialling any of the murderous documents which were submitted for his approval.
He died in hospital at Lindau am Bodensee on 4 August 1951 soon after his release.