Karl studied law at London, Paris, Bonn and Berlin, and was awarded a Dr. jur.

During and after the Revolution he opposed the establishment of a far-left Räteherrschaft (rule by workers' and soldiers' councils), at the cost of being at times subject to physical violence.

[1] From May 1921 to April 1933, Jarres was a member of the Prussian State Council and served as its Second Vice President from May 1921 to January 1924.

[4] During the Occupation of the Ruhr in 1923 Jarres was deposed as mayor by the military authorities and served a deportation order by the Belgians.

Strongly nationalistic feeling (he was a Burschenschaft member) and a dedication to liberty made him one of the most ardent supporters of the Versackungspolitik (leaving sole responsibility for the Ruhr to the occupiers).

After the Ruhr crisis was over, Jarres loyally supported the policies of Stresemann (now Foreign Minister).

When the Great Depression hit the city, relying mostly on heavy industry (coal and steel), was severely affected and Jarres could do little to prevent unemployment from rising.

[1] Reelected in 1930, Jarres was deposed as mayor by the Nazis on 5 May 1933 and in November formally retired from public life (im Ruhestand).

As a leading industrialist, he was appointed by Minister President Hermann Göring to the newly reconstituted Prussian State Council on 11 July 1933 and served until the fall of the Nazi regime.