There, he found his friends from Sadiki such as Habib Bourguiba, Mahmoud El Materi, Bahri Guiga, Mustapha Baffoun and Sadok Boussofara.

He returned to Tunis in 1928 to start working as a lawyer in parallel with numerous other activities: Political economy lessons in El-Khaldounia and writing newspaper articles in Arabic or French, such as La Voix du Tunisien and L'Action Tunisienne, which he founded with Bourguiba, El Materi and Guiga, in 1932.

The new party wanted itself to be modernist in its methods and organization, but at the same time, educator and mobilizer of the low classes for a better awareness of the need to rid the country of colonialism.

After the arrival of Armand Guillon, the new resident-general of France in Tunisia, Sfar was freed in April 1936 at the same time as the other members of the party leadership.

Before he died, Sfar published in the French feminist journal Leïla of December 1939 an article strongly denouncing Adolf Hitler's regime and explaining the danger that he represented for humanity.

If such plans were realized, it is the end of civilization; it is the end of progress, but we can predict for sure, the failure of such an attempt; because humanity follows, in general, a line of evolution that no force in the world can or could divert its course; and all institutions, like the "German family" who oppose this evolution are assured of a fast and certain disappearance.Struggling for the independence of his country, Tahar Sfar also advocated for a real cooperation between the Eastern and Western world, as he wrote in the early 1930s: "Peace in the future, progress of the entire humanity depend on this union, this narrow collaboration between East and West, who, instead of turning their backs on themselves, ignore themselves, ought, on the contrary, support each other, provide mutual aid and cooperation for the rehabilitation of the fate of humanity.