The Joliot-Curies had become increasingly aware of the growth of the fascist movement. They opposed its ideals and joined the Socialist Party in 1934, the Comité de vigilance des intellectuels antifascistes a year later, and in 1936 they actively supported the Republican faction in the Spanish Civil War. In the same year, Joliot-Curie was appointed Undersecretary of State for Scientific Research by the French government, in which capacity she helped in founding the Centre National de la Recherche Scientifique. 
Frédéric and Irène visited Moscow for the two hundred and twentieth anniversary of the Russian Academy of Science and returned sympathizing with Russian colleagues.  Frédérics close connection with the Communist Party caused Irène to later be detained on Ellis Island during her third trip to the US, coming to speak in support of Spanish refugees, at the Joint Antifascist Refugee Committees invitation.
The Joliot-Curies had continued Pierre and Marie's policy of publishing all of their work for the benefit of the global scientific community, but afraid of the danger that might result should it be developed for military use, they stopped: on 30 October 1939, they placed all of their documentation on nuclear fission in the vaults of the French Academy of Sciences, where it remained until 1949.
Joliot-Curies political career continued after the war and she became a commissioner in the Commissariat à lénergie atomique. However, she still found time for scientific work and in 1946 became director of her mothers Institut Curie'.
Joliot-Curie became actively involved in promoting womens education, serving on the National Committee of the Union of French Women (Comité National de lUnion des Femmes Françaises) and the World Peace Council. The Joliot-Curies were given memberships to the French Légion dhonneur'; Irène as an officer and Frédéric as a commander, recognising his earlier work for the resistance.