At first he was closely associated with Louise Michel, but he soon became a major figure in his own right, and one of the best-known anarchists in the country. In 1894 he was one of the defendants in the Trial of the Thirty, when the French authorities tried unsuccessfully to suppress the anarchist movement by implicating its leaders in criminal conspiracies, and was acquitted. He was involved in several papers at various times in several parts of France, the most important of which was Le Libertaire (The Libertarian), which he started with Louise Michel in November 1895 and which appeared weekly on and off until June 1914. He was active in the Dreyfusard movement, replacing Le Libertaire with the daily Journal du Peuple during 1899. He also produced Le Quotidien (The Daily) in Lyon during 1901-1902. From 1903 he was active in the birth-control movement. From 1904 to 1917 he ran a libertarian school called La Ruche (The Beehive) at Rambouillet (near Paris).
After the war he revived Le Libertaire, which continued from 1919 until 1939. In 1921 he led the reaction in the French anarchist movement against the growing Communist dictatorship in the Soviet Union. In January 1922 he began La Revue Anarchiste (Anarchist Review), the leading monthly magazine of the French anarchist movement between the world wars. In the late 1920s he opposed the sectarianism both of the authoritarian Platformists and of their critics, and advocated what he called an `Anarchist Synthesis' in which individualism, libertarian communism and anarcho-syndicalism could co-exist. In 1927 he led a secession from the national Union Anarchiste, and in 1928 he helped to found the Association des Federalistes Anarchistes and to begin its paper, La Voix Libertaire (Libertarian Voice), which lasted from 1928 until 1939. He was reconciled with the national organisation and Le Libertaire in 1934. During the 1930s he took part in the peace movement as a prominent member of the International League of Fighters for Peace. In 1940 he took refuge from the war in Royan (near Bordeaux), where he died in 1942.