Delacour was born in Paris into an aristocratic family and grew up on the family estate at Villiers near Amiens where he was fascinated by the orchids and ornamental birds in the castle park. With the money he received from his family, he established a private zoo in Picardy. He attended good schools in Paris where he spent time in the natural history museum and received a doctorate in biology from the Université Lille Nord de France. He maintained 1345 birds of 344 species in 1916. He served in the French Army during the First World War, a war which devastated the family estate, as well as killing his only surviving brother. He was so shocked by the inhumanity that he swore not to have a family and moved to England for its peace. He however decided to return to France and bought the Chateau Clères in Normandy where he set about making a menagerie. It was so well known that the 9th International Ornithological Congress was held in 1938 in the nearby town of Rouen. One of the visitors to his aviary was Pierre Jabouille, the French administrator for Annam. On his invitation, he went on numerous scientific expeditions to Indochina, particularly Vietnam, as well as to Venezuela, the Guianas and Madagascar. During the Second World War Chateau Clères was bombed by the German Luftwaffe on 7 June 1940. Most of his library, animals in his collection and the castle were destroyed but his manager Frank E. Fooks escaped. Delacour was saved by Belgians and Frenchmen and escaped to Vichy. Erwin Stresemann, a good friend and admirer of Delacour heard of the fate of the zoo and attempted to ensure the safety of the remaining animals through the Wehrmacht. Delacour meanwhile fled through Casablanca, Rabat, Tangier and Lisbon, reaching New York on Christmas Day 1940. His American friends found him a job, his first, at the Bronx Zoo and the Museum of Natural History at New York. Delacour lived in the United States, working as a technical adviser for the New York Zoological Society as well as on avian systematics at the American Museum of Natural History examining many enigmatic genera such as Hypocolius and Picathartes. In 1952 he became director of the Los Angeles County Museum of History, Science and Art, retiring in 1960. After the war ended he divided his time seasonally, spending every summer from 1946 at his estate at Clères where he organized the rebuilding of his zoo through his assistant F.E. Fook and with assistance from Sir Peter Scott, Alfred Ezra and the Duke of Bedford. It was opened in May 1947 with the French Prime Minister taking part in the inauguration. The collection was eventually donated to the Museum National d'Histoire Naturelle in 1967. He was a co-founder of the International Council for Bird Preservation, serving as its president from 1938 to 1958. Delacour spent his winters in the United States, mainly in Los Angeles where he served from 1952 to 1960 as the director of the County Museum of History, Science and Art. Spending all his time and resources on his bird collections, he never married. He had trained as an operatic singer and was particularly fond of Moussorgsky's compositions. He was restricted to a wheelchair in later life. He lived with his mother who died in 1954 at the age of 94. In his autobiography "The Living Air" he wrote that humans would eventually annihilate all life on earth. Delacour is commemorated in the scientific name of a species of Southeast Asian snake, Plagiopholis delacouri.
