He was also an anarchist, anarcho-syndicalist, anti-colonial activist and fierce opponent of nationalism and the Communist state, in addition to being a writer and volunteer in the International Group of the Durruti Column during the Spanish Civil War.

He then moved to France, where he was an activist in the recently rebuilt Union Anarchiste (UA) and the Confédération Générale du Travail-Syndicaliste Révolutionnaire (CGT-SR) and with his friend Sliman Kiouane was founder (in 1923) of the Committee for the Defence of Indigenous Algerians, one of the first national liberation movements in French North Africa.

Sail Mohamed was also a passionate anti-Stalinist, and, following his arrest in 1932, he rejected support from Red Aid, a front organisation of the French Communist Party.

Sail Mohamed was arrested and jailed for 4 months following an incident where he was found collecting and hiding arms for workers' movements that had risen up as a result of a fascist and anti-Semitic demonstration that occurred on 6 February 1934 in France.

Sail would later escape by forging false papers and would spend the war underground, attempting to revive anarchist movements in occupied France.