[1] When Nazi-Germany occupied France in 1940, Pablo stayed in Paris where he organized illegal propaganda and was involved in the re-construction and re-unification of the French Trotskyist movement, which was operating underground into the Provisional European Secretariat of the Fourth International.
[2] By 1944, Pablo was fully involved with the movement, and was elected the organizational secretary of its European Bureau, which had re-established contact between the Trotskyist parties.
After the war, Pablo became the central leader of the Fourth International (FI) with the support of the SWP of the United States and James P. Cannon.
In the uncertain aftermath of World War II, when the Trotskyists were numerically dwarfed by the mass communist parties and their hopes for a revolutionary breakthrough were dashed, Pablo also advanced a new tactic for the FI from its third world-congress in 1951 onward.
[7] Inspired by the Cuban Revolution as well as the Tito–Stalin split demonstrating that the Stalinist Communist Parties may not unalterably subordinate to Stalin, Pablo also started to argue that even the Stalinist parties who were in power in various countries at the time could be pushed into taking leadership in revolutionary conflicts by the mass activity of the working class, which caused further controversy and division within the ranks of the FI.
Pablo writes: "the rise of Communist Parties to power is not the consequence of a capacity of Stalinism to struggle for the Revolution, does not alter the internationally counter-revolutionary role of Stalinism, but it is the product of an exceptional combination of circumstances which has imposed the seizure of power either upon the Soviet bureaucracy (in the case of the European buffer zone) or upon certain Communist Parties (Yugoslavia, China)".
[8] The central document emphasized the basic role of workers' democracy, not only as political factor, but also as indispensable for economic development.
The congress insisted on the necessity for the Trotskyist movement, especially in the imperialist countries to devote a large part of its activity to aiding colonial revolution.
In 1959 he set up and operated a secret munitions factory, hidden within a citrus plantation in the Moroccan city of Kentire, where they manufactured a lightweight version of the Sten submachinegun while also overseeing a workshop on the Dutch-German border that produced counterfeit passports and cash to support the FLN.
Pablo was also part of a four-man committee tasked with drawing up a decree concerned with property that had been seized by the Algerians after the French colonials had fled the country.
[2][5] Meanwhile, in 1963, ICFI groups around the Socialist Workers Party (SWP) were moving back towards unity with the ISFI, sharing common positions towards the Cuban revolution.
[14] During the Colonels' dictatorship in Greece in 1967 Pablo, together with Andreas Papandreou, established a network to assist resistance members' escape abroad.
[2] This group dropped the reference to the Fourth International during its meetings in 1972 and at the same time proclaimed it no longer considered itself Trotskyist nor a party of world revolution.
[15] In 1979, the TMRI would send an open letter to members of the Fourth International, calling for the need to "develop new directions, new forms of struggle and of organization" as well as "the elaboration of a transition program based on socialist autogestion".
[14] After the fall of the Greek Junta, Pablo returned to Greece, played a role in the founding of the Pan-Hellenic Socialist Party (PASOK) and, from 1981, served as Special Advisor to Prime Minister Andreas Papandreou; The sections of the IRMT rejoined the reunified Fourth International in 1994 and 1995, although the agreement was not applied in Pablo's individual case.