Before becoming a journalist, he had several casual jobs, including being depicted as a soldier on a good-luck card for a postcard seller, belying his future pacifism.
He was arrested in November 1939, at which time he had already joined his regiment in Meaux, for articles which had appeared in March and August 1939, and for having signed Louis Lecoin's tract "Paix immédiate".
In November 1940, the German authorities pressured him to take a public position against the Jews and in favour of the politics of collaboration with the Vichy regime.
to illustrate the contradictions and compromises of absolute pacifism: the willingness to seek an understanding with Germany to avoid war, transforming, after France's defeat, into a desire for proper coexistence, even offering to serve the Germans.
The newspaper Aujourd'hui was far from being innocent in its hunting down those allegedly responsible for France's defeat, resorting to the "clean sweep of the broom" myth in its Anglophobia.
He left the editorship of le Canard enchaîné in April 1947, following an article which was cut, on the subject of "Aragon, Elsa Triolet, Maurice Thorez and the communists".
Jeanson abandoned cinema in 1965 to devote himself to polemical journalism and the editing of his memoirs, which were published under the title 70 Ans d'adolescence several months after his death.
His theatrical works include Amis comme avant, Aveux spontanés, Le Petit Navire, Toi que j'ai tant aimée and L'Heure éblouissante.