During the rule of the Nazi Party, Hermes was part of the right-wing resistance, for which he was imprisoned and sentenced to death, but never executed thanks to the intervention of his wife.

In 1905/06 Hermes was awarded a doctorate at Jena with a dissertation on the optimization of crop rotation and then became a research associate at the animal breeding department of the Deutsche Landwirtschaftsgesellschaft (German Agricultural Society) in Berlin.

With the start of World War I, he returned to Germany and worked first for the general staff, then in several functions in the bureaucracy in charge of the national food supply (Kriegsernährungswirtschaft), including organising the cultivation of oil seed in the Danube district and in the area near Lake Constance.

[1][3] After the end of the war, in 1919, Hermes headed the department on agriculture and forestry of the Reichswirtschaftsministerium (Ministry of Economic Affairs).

In 1930, he became president of the Reichsverband der deutschen landwirtschaftlichen Genossenschaften-Raiffeisen (National Association of German Agricultural Cooperatives).

He returned to Germany to collect his family, but the eruption of World War II prevented his departure back to South America.

Immediately after 20 July 1944 he was arrested and on 11 January 1945 sentenced to death for being an active member of the conspiracy to kill Hitler.

As a result of his attempts to lead a pan-German policy and his refusal to agree to the so-called Bodenreform, he was deposed on 19 December 1945 by the Soviet occupation forces as chairman of the CDU.

He founded the Gesellschaft für die Wiedervereinigung Deutschlands (Society for the Reunification of Germany) placing himself in opposition to the views of Konrad Adenauer.

[1][3] In 1947, Hermes became a member of the Bizonal Economic Council (Wirtschaftsrat des Vereinigten Wirtschaftsgebietes), as chairman of the food committee.

In 1949, he founded the Godesberger Kreis, an organization working towards the reunification of Germany and an improvement in political relations with Eastern Europe, views that were highly controversial in the CDU at that time.