[citation needed] He wrote for numerous media outlets in the 1940s and 1950s including Het Parool, Le Peuple, l'Observateur and Agence France-Presse.
At the height of the Cold War, he publicly defended the merits of Marxism in debates with the social democrat and future Dutch premier Joop den Uyl.
He and his comrades were expelled from the Socialist Party not long after the Belgian general strike of 1960–61 for opposing its coalition with the Christian Democrats and its acceptance of anti-strike legislation.
Only from 1968 did Mandel become well known as a public figure and Marxist politician, touring student campuses in Europe and America giving talks on socialism, imperialism and revolution.
Mandel had been granted visas in 1962 and 1968 but had violated the conditions of his second visit unknowingly by asking for donations for the defence in the legal cases of French demonstrators.
[6] Mandel campaigned on behalf of numerous dissident left-wing intellectuals suffering political repression, advocated for the cancellation of the Third World debt, and, in the Mikhail Gorbachev era, spearheaded a petition for the rehabilitation of the accused in the Moscow Trials of 1936–1938.
When in his seventies, he travelled to Russia to defend his vision of democratic socialism and continued to support the idea of Revolution in the West until his death.
[9] Mandel is probably best remembered for being a populariser of basic Marxist ideas, for his books on late capitalism and Long-Wave theory, and for his moral-intellectual leadership in the Trotskyist movement.
Despite critics claiming that he was "too soft on Stalinism", Mandel remained a classic rather than a conservative Trotskyist: writing about the Soviet bureaucracy but also why capitalism had not suffered a death agony.