However illness found him in France when the Second World War began. The same ill health meant that until 1944 he played little part in the activities of the french Trotskyists although he is reported to have given educational classes to David Korner's Union Comuniste.
By 1944 he was fully involved with the movement and was elected to the newly formed leadership of the European Trotskyists who had recently established contact with each other. From this body he became a member of the International Executive Committee of the Fourth International when the war had ended.
Indeed at the end of the war Pablo and Ernest Mandel, often known as Germain in this period, became the central leaders of the Fourth International with the blessings of the SWP of America and JP Cannon himself. In this capacity they jointly sponsored a faction within the british movement that opposed the leadership of Jock Haston in the RCP. The result was the collapse of the RCP as an independent force.
Pablo and Mandel were instrumental in these years of winning the Fourth International to a position that asserted that the Eastern European states conquered by the Soviet Armed Forces in 1944-45 had become what they described as Deformed Workers' States and for the expulsion of comrades who disagreed with this thesis from the FI.
Pablo also began to develop a new strategy for the FI from 1951 onwards. He argued that a Third World War, which was seen as being imminent, would be characterised by revolutionary outbreaks during the actual war. This thesis of War/Revolution meant that to overcome their small numbers the Trotskyists should join, or in Trotskyists terminology enter, the mass Communist or Social Democratic (Labour) parties. This was known as entrism sui generis or long term entry.
In 1953 the American, British and part of the French Trotskyists declared themselves in opposition to this course of action and left the FI to form the International Committee of the Fourth International. The hostility of the ICFI to what became known as Pabloism became notorious. Pablo continued with what was now known as the International Secretariat of the Fourth International.
As the 1950s became the 1960s Pablo became more convinced that revolutionary prospects were best pursued in what was to become known as the third World of Africa, Latin America and Asia. Therefore he was personally closely involved in supporting the Algerian national liberation struggle against France. This would lead to a period of imprisonment.
By 1963 however the ICFI forces around the SWP of the USA were moving back towards unity with the ISFI and Pablo was a barrier to that unification. The reunification that was achieved in 1963 rapidly led them to oust Pablo from the FI at the head of its so called African Bureau in 1964.
Nonetheless Pablo was not willing to leave revolutionary politics and organised the Revolutionary marxist tendency to fight for his ideas. Most of the supporters of this and the International Revolutionary Marxist Tendency were based in France but it eas never an organisational competitor with the larger Trotskyist groups. Pablo's influence from this time then was mainly through his writings.
Most central to those ideas in the 1970s was his advocacy of autogestion which is often translated into English as workers control. However it would seem to mean something rather different to the traditional understanding of workers control of production as understood in the workers movement. By the 1980s however Pablo had been relegated to the past. Unusually for a revolutionary his funeral was a state event in his native Greece which circumstance is explained by his friendship from the 1930s with Andreas Papandreou who had been a Trotskyist in his youth.