Pierre Daye was in charge of foreign politics in the Nouveau Journal, a newspaper supporting the National Socialist thesis created in October 1940 by Paul Colin and under the direction of Robert Poulet. Daye was one of the shareholders of the Editions de la Toison d'Or created during the war (out of a total of 150 shares, 135 were owned by the Slovak group Mundus, which was responsible to the Reich Foreign Affairs Minister headed by Joachim von Ribbentrop.) Daye was also a correspondent of Je suis partout, the ultra-collaborationist French language review headed by Robert Brasillach. He was sentenced to death as a collaborator on December 18, 1946, by the Brussels War Council.
After the war, he fled to Argentina with the help of Charles Lescat, also collaborator of Je suis partout. There, he took part in the meeting organized by Juan Perón in the Casa Rosada during which a network (colloquially called ratlines) was created, to organize the escape of collaborationists and former Nazis. On June 17, 1947, Belgium requested his extradition from Argentina, but the extradition request was not filed. Along with countryman René Lagrou and other European figures such as the academic Jacques de Mahieu Daye became central to the Nazi escape routes.
In Argentina, Pierre Daye resumed his writing activities, becoming the editor of an official Peronist review. He then returned to Europe where he wrote his memoirs.