From 1933 onwards, he was a political economist for the Fascist National Front and from 1938 to 1939 Chairman of the Board of the newspaper, Neue Basler Zeitung.
In July 1940, after the defeat of France against Germany, Kellermann and his fellow-citizens came to the hope of an upsurge of right-wing forces, the so-called second ‘’Frontenfrühling [de]’’, a term used by Swiss fascists to describe the predicted surge in fascism, referring back to the first Frontenfrühling in 1933.
On 10 October 1940, under the leadership of Klaus Hügel in Munich, a conference was held with the leaders of the front, Hans Oehler and Benno Schaeppi [de] of the Bund treuer Eidgenossen nationalsozialistischer Weltanschauung [de] (BTE) (Confederation of Loyal Confederates of the Socialist Weltanschauung), Ernst Burri and Arthur Leonhardt of the Schweizerische Gesellschaft der Freunde einer autoritären Demokratie [de] (SGAD) (Swiss Society of Friends of an Authoritarian Democracy).
For lack of evidence, he was released on bail, whereupon he left Switzerland in November 1941 for Germany, where he became director of the Reichswerke Hermann Göring in Berlin and in Weimar.
After the war, Keller returned to Switzerland and was condemned to a total of 14 years for breaching military secrets and attacking the independence of the Swiss Confederation.