Bleibtreu was born during his family's refuge in Marseille from wartime bombing, Marcel Bleibtreu became a radical thinker as a child. After studies at the lycée Condorcet, he studied medicine in Paris, and graduated in 1947. He joined the Groupe Bolchevik Léniniste, the Trotskyist organisation, in September 1936. By 1944 the GBL had merged with two other Trotskyist currents to form the Internationalist Communist Party, (PCI), the French section of the Fourth International. Bleibtreu led workplace cells of the PCI around Puteaux-Suresnes-Nanterre under the pen-name Pierre Favre. In November 1944, he became an editor of the party's journal, La Vérité. He was named general secretary of the PCI in 1946, and led the party's growth after its post-war legalisation.
In 1954 the Algerian War of Independence escalted. The PCI naturally supported independence. However, Lambert and Bleibtreu started to disagree over tactics in Algeria. Lambert supported the MTLD of Messali Hadj while others, along with Bleibtreu, supported CRUA (the fore-runner of the FLN). Lambert was able to win a majority in 1955, expelling Bleibtreu and its comrades. The expelled group took again the name Goupe Bolchévik-Leninist and publish the review 'Trotskysme '. The GBL later joined the New Left, within which Bleibtreu created the Revolutionary Socialist Tendency, a founder member of the UGS and the PSU. Bleibtreu became a member of the political committee of the PSU, then also its general secretary until he left that party in 1964.
Bleibtreu's militancy engaged art as well. He organized in Paris, in 1967, an exhibition named "Art for Peace to Vietnam", a method which he would use again, in 1993, in Athens against the embargo in Iraq.
Bleibtreu supported the development and the coordination of the 'Base Committees' in 1968, endeavouring to reduce the disagreements between the Trotskyist groups, from where his nickname of "Jean XXIII of Trotskyism" comes, following a famous appeal he made in the large lecture theater of the Sorbonne. Bleibtreu was a militant in various associations, in particular in S.O.S Children of the South, and the coordination for the lifting of the embargo imposed on Iraq, which he directed.
- Biography and Inventory of the Fonds Marcel Bleibtreu at the Bibliothèque de Documentation Internationale Contemporaine