When France surrendered to Nazi Germany in June 1940, Déricourt went back to civil aviation but in August 1942 he escaped to Britain. After being checked out at the Royal Patriotic School's vetting process, he joined the Special Operations Executive (SOE).
Déricourt was parachuted into France on 22nd January 1943. His main task was to find suitable landing grounds and organize receptions for agents brought by air. He worked mainly for the Prosper Network and over the next few months he arranged the transport by plane of over 67 agents including Noor Inayat Khan, Vera Leigh, Yolande Beekman, Eliane Plewman, Diana Rowden, Jack Agazarian, Francis Suttill, Pearl Witherington and Lise de Baissac.
In the summer of 1943 the Gestapo arrested several British agents working in France. It became clear that a double-agent had infiltrated the Special Operations Executive. Several agents, including Francis Cammaerts, Jack Agazarian and Francis Suttill became convinced that Déricourt was the man responsible. These suspicions increased when it became known that Déricourt was living in Paris in a flat next to one rented by Hugo Bleicher of Abwehr.
Another agent, Henri Frager, told Nicholas Bodington when he visited occupied France in July 1943 that Déricourt was a German spy. Bodington dismissed this theory arguing that as Déricourt arranged his journey to France and he had not been arrested. When Bodington refused to take action some agents began to think that he was also a double agent.
Soon afterwards Georges Pichard, informed Maurice Buckmaster that he had heard from a good source that a "Frenchman in charge of air operations in the Paris and Angers districts" was working for Abwehr. Buckmaster like Bodington before him, dismissed the charges and Déricourt was allowed to continue his work in France until February 1944.
After the Second World War the interrogation of German officials provided evidence that Déricourt was guilty of providing information to Abwehr and the Gestapo that led to the arrest and execution of several agents including Noor Inayat Khan, Vera Leigh, Yolande Beekman, Eliane Plewman, Diana Rowden, Gilbert Norman, Jack Agazarian and Francis Suttill.
In November 1946, Déricourt was arrested by the French authorities but did not appear in court until June 1948. At the trial Nicholas Bodington testified that he had been in charge of all Déricourt's work in the field. He admitted that he was aware that Déricourt was in contact with the Germans but that no important information had been revealed.
During the trial the defence council argued that although the prosecution could bring plenty of suspicious indirect evidence against Déricourt, they could not actually pin any definite act of treachery on him. Largely on the evidence provided by Nicholas Bodington, Déricourt was acquitted.
When Jean Overton Fuller interviewed Déricourt for her book, Double Agent, he told her that leaders of the Special Operations Executive knew the organization had been penetrated by the Gestapo and that men and women were deliberately sacrificed in order to distract their attention from the planned landings in Sicily and Normandy.
Henri Déricourt was reported to have been killed in an air crash while flying over Laos on 20th November, 1962. His body was never found and some writers have claimed that his death was faked in order to allow him to begin a new life under another name.