In 1940 De Maistre started work for the French Section, Joint War Organization of the British Red Cross Society and the Order of St John, London. In 1942 he was posted to Foreign Relations Department, British Red Cross Society. During this time de Maistre scarcely painted. After World War II, however, he had become an artist of the establishment. He had no trouble selling his paintings, and continuing to accept private commissions for society portraits. His work was also part of the painting event in the art competition at the 1948 Summer Olympics.
