He often visited the Maison du Peuple in Chambon, where he participated in theatrical productions and read widely in the library.

He was placed in the auxiliary service due to his myopia, and was in the clothing store of the 30th Artillery Regiment in Orléans at the outbreak of World War I (1914–18).

[1] Frachon was returned to active duty in the Guérigny naval arsenal, but due to his technical skills was not sent to the front.

Frachon disagreed with the CGT position of supporting the Union sacrée, under which no industrial actions were taken during the struggle with Germany, and preferred Alphonse Merrheim's opposition to contributing to the war effort.

[1] Frachon returned to Chambon-Feugerolles on 8 September 1919, where he joined the socialist Section Française de l'Internationale Ouvrière (SFIO).

After the split of the SFIO at the Tours Congress of 25–30 December 1920 he became a member of the local branch of the French Communist Party.

[2] In June 1921 Frachon returned to Chambon where he found work with the Société anonyme des aciéries et forges de Firminy.

In this role he participated in the founding congress of the Confédération générale du travail unitaire (CGTU) on 26 June – 1 July 1922 in Saint-Étienne.

In November 1924 Frachon was appointed permanent secretary to the Loire departmental union of the Confédération générale du travail unitaire (CGTU).

[2] In 1925 he became secretary of the PCF trade union committee covering the departments of the Rhône, Loire, Saône-et-Loire, Haute-Loire, Ain, Jura, Ardèche, and part of Isère.

As secretary of the departmental union of the CGTU he was a member of the French delegation to the sixth session of the Executive Committee of the Communist International in Moscow in February–March 1926.

He was very active in promoting the party in meetings throughout the region, fighting Trotskyist influences and praising the example of the Soviet Union.

Frachon ran unsuccessfully in the national elections in April 1928 as candidate of the Workers and Peasants Bloc for the 3rd district of Lyon.

[1] Frachon attended the PCE national conference in June 1928, where he was designated delegate to the 6th congress of the Communist International in July–September 1928.

Frachon and other PCF leaders were arrested on 24 July 1929 at a meeting held in Villeneuve-Saint-Georges to prepare for the international anti-war demonstrations of 1 August.

Eugen Fried was assigned by Comintern to eliminate the social-democratic and anarcho-syndicalist elements, and prevent the Trotskyists from gaining influence.

He was to resolve rivalry, eliminate unsound elements and install men loyal to Moscow at the head of the party.

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

Frachon became secretary of the reunited Confédération générale du travail (CGT) at the trade union unification congress in Toulouse in March 1936.

On his way back, in Washington, D.C. he gave an interview to United Press in which he denounced concessions made to fascism during the crisis over German demands of Czechoslovakia.

The Molotov–Ribbentrop Pact between the Soviet Union and Germany on the eve of World War II (1939–45) caused a surge of anti-communist feeling.

On 8 October 1939 he was designated PCF secretary for French territory at a leadership meeting in Belgium which he did not attend for fear of being detained at the border.

[1] Arthur Dallidet, Jeanjean, Georgette Cadras, Jeannette Tétard and Claudine Chomat left Paris for the south at the same time, and met Frachon in Haute-Vienne.

[8] After the armistice of 22 June 1940 the PCF leaders denounced the imperialist war, called for peace and concentrated on opposition to the Vichy government.

[9] Tréand and Jean Catelas, the deputy for Amiens, began negotiations with the German ambassador for permission to resume open publication of the communist journal l'Humanité.

[1] They decided not to use the safety devices and hideouts that Maurice Tréand had put in place, but to use a new network established by Dallidet.

[11] In the autumn Frachon and Duclos decided to appoint Charles Tillon to organize the first armed groups of the PCF.

He contacted Louis Saillant in the autumn of 1940, who was also hostile to the draft Charte du Travail and to collaboration with the enemy.

Frachon proposed to Léon Jouhaux a joint appeal to the working class, calling on them to demand their union rights, refuse the Charte du Travail and forced labor in Germany, urge them to join the armed struggle and announce the reunification of the CGT.

He laid out the task of CGT union officials: to bring the war to a successful end, rebuild the economy and resume the fight for worker's rights.