While in exile in London between 1940 and 1944, Pierlot served as both Prime Minister and Minister of Defence and played an important role in wartime negotiations between the Allied powers, laying the foundation for Belgian post-war reconstruction. After the liberation of Belgium in September 1944, Pierlot returned to Brussels where, against his wishes, he headed a fresh government of national unity until February 1945. Criticism from the political left and the failure of the new government to deal with the serious issues facing the country following the liberation led to the fall of the government in February 1945 and he was replaced by the socialist Achille Van Acker. Pierlot's stance against Leopold III during the war made him a controversial figure during his lifetime and he was widely disliked in the same royalist and conservative circles from which his own Catholic Party (later the Christian Social Party) drew most of its support. He retired from politics in 1946 amid the crisis of the Royal Question, surrounding whether Leopold could return to the Belgian throne, and died peacefully in 1963. After his death, Pierlot's reputation improved as the decisions he took during the war were reconsidered by historians.