[1] Hénaff joined the Confédération générale du travail unitaire (CGTU) in 1924, and then the French Communist Party (PCF).

Hénaff and Benoït Frachon, the national representatives, provided assistance to the local militants Auguste Walch, Frédéric Fassnacht, Joseph Mohn and Georges Woldi.

Hénaff' pleaded in L'Humanité in November 1933 for French workers to welcome their German comrades, and to "break the existing xenophobic currents.

[1] After the outbreak of the Spanish Civil War in 1936 Hénaff, Jean Zyromski and Georg Branting of the Commission Européenne d'Aide à l'Espagne published a manifesto that said, "The Spanish people would have already suppressed the Fascist rebellion if the rebel leaders had not been able to obtain, and did not still obtain, war matériel from international Fascist organizations.

[1] A confidential police report on a clandestine meeting of communist militants on 24 July 1940 gave the attendees as Jean Catelas, former Deputy of the Somme, Hénaff and others.

[5] Hénaff, André Tollet and Jean-Pierre Timbaud began to form popular committees in the work places and clandestine unions.

[7][a] Other prisoners who escaped from the camp on 18–19 June 1941 were Fernand Grenier, Henri Raynaud, Léon Mauvais and Roger Sémat.

[8] Hénaff resumed his underground activities under the pseudonym "Denis", and joined the leadership of the PCF's Organisation Spéciale, where he was responsible for coordinating between the various armed units.

[9] Soon after Arthur Dallidet introduced him to Hénaff, who was responsible for the armed struggle under the direction of Charles Tillon.

[10] To avoid growing risk of arrest, Hénaff moved in 1943 with his wife and children from Paris to Lyon, where he directed the underground unions in the southern zone and liaised between the FTP and the Main-d'œuvre immigrée (MOI).

At first, Hénaff tried to suppress the movement, calling the leaders "Gaullist-Trotskyite Anarchists" and "Hitlero-Trotskyite provocateurs in the pay of de Gaulle."