In 1942, they formed fighting units to assassinate German leaders and soldiers among the occupation forces; perform acts of sabotage on railroads and other transportation infrastructure being used to transport people and goods being taken from France to Germany; and to help organize sabotage in factories forced to produce armaments and goods for the German military.

It engaged mainly in propaganda, editing reviews, fabricating false identity documents, supporting clandestine organizations logistically, and sabotaging German and Vichy facilities and capabilities.

It was a member of the Conseil national de la Résistance (CNR), which federated, under Jean Moulin's authority, various Resistance movements, beginning in the middle of 1943.

Pierre Villon stated: "The FN is the only movement where we have finally reconciled the parish priest (curé) and the teacher, the Parti Social Français and the Communist, and the Radical with the Socialist.

The 4 September 1942 Law on the STO (Service du travail obligatoire), signed by Pierre Laval, the head of government in the Vichy régime, proposed to exchange one prisoner-of-war for three Frenchmen to go to work in Nazi Germany.