In 1935, together with the poet Attila József and the publicist Pál Ignotus, he founded the anti-fascist and anti-Stalinist literary journal Szép Szó.

After the war, Fejtő attended the Congrès des intellectuels pour la liberté, alongside Raymond Aron, François Bondy, and David Rousset.

The publication in 1952 of his book A History of the People's Democracies (translated in seventeen languages and re-edited several times) earned him suspicion on the part of several intellectual figures close to the French Communist Party.

He also contributed to numerous French and non-French journals and newspapers, including Esprit, Arguments, Contre-Point, Commentaire, Le Monde, Le Figaro, La Croix, Il Giornale, La Vanguardia, Magyar Hírlap and The European Journal of International Affairs.

Close friends with Nizan, Mounier and Camus, critical interlocutor of Malraux and Sartre, he met with leaders of the Comintern and the Communist movement, talked to the masters of the Kremlin, to Tito, Castro and Willy Brandt, and both admired and criticized Charles de Gaulle and François Mitterrand.