In the period before World War II (1939–45) began he first opposed and then supported letting refugees from Nazi Germany work freely in France.

[4] The Radicals had agreed not to oppose René Plard in the 1st district of Troyes, and in return Gentin was supported by the Amis du Rappel.

[1] At the annual Radical Party congress in Marseille at the end of October 1938 Gentin proposed a modern economic plan with partial funding from the state.

[6] With the economy still depressed, in the late 1930s there were popular demands for measures to prevent Jewish and other refugees from Nazi Germany from competing with native French people.

[7] The local chambers of commerce had to agree that a foreign-owned enterprise was "desirable", and could limit the number of foreigners who could work in some commercial occupations.

He sponsored the 21 April 1939 "Decree to Favor the Establishment in France of Industries of National Interest", which had resulted from lobbying by Louise Weiss and the Bonnet Committee.

[12] After the defeat of France, on 10 July 1940 Gentin voted in favor of granting the constitutional powers requested by Marshal Philippe Pétain.

[1] Gentin was retained by the Vichy government as mayor of Isle-Aumont during the German occupation of France, and continued to run his printing house.

[13] It was said at his trial, "M. Gentin derived from his functions as political director substantial pecuniary advantages, and he also maneuvered as administrator to profit from the particular conditions created by the German occupation.