En 1932, comenzó una asociación de por vida con el Museo Americano de Historia Natural (AMNH) en la ciudad de Nueva York trabajando allí como voluntario. En 1933, fue empleado allí como asistente y posteriormente pasó por toda la gama de ascensos, para convertirse en Curador de Aves en 1963, muriendo inesperadamente en el cargo dos años más tarde, a los 53 años, de un repentino ataque al corazón.
Además de numerosos artículos en las publicaciones científicas de AMNH, escribió muchos artículos ilustrados para Natural History y para National Geographic Magazine.
Publicó Living Birds of the World (1958), Birds of Paradise and Bower Birds (1969), y coautor (con Austin L. Rand) del Handbook of New Guinea Birds (1967).
Gilliard fue un experto fotógrafo y cinematografista; participando en la realización del documental Search for Paradise (1957), dirigido por Otto Lang.
Birds of Paradise and Bower Birds, The World Naturalist, 1966
National Audubon Society Nature Program: Birds of the South Pacific, Nelson Doubleday, 1956
The birds of Mt. Auyan-Tepui, Venezuela, Am. Museum of Natural History, 1941
On the breeding behavior of the cock-of-the-rock (Aves, Rupicola rupicola), Am. Museum of Natural History, 1962
Game birds of the world (Nature program), N. Doubleday, 1958
Living Birds of the West, Doubleday, 1958
Results of the 1958–1959 Gilliard New Britain Expedition, Am. Museum of Natural History, 1967
Annotated list of birds of the Adelbert Mountains, New Guinea, Am. Museum of Natural History, 1967
Birds of the South Pacific, Doubleday, 1956
A comparative analysis of courtship movements in closely allied bowerbirds of the genus Chlamydera, Am. Museum of Natural History, 1959
The ecology of hybridization in New Guinea honeyeaters (Aves), Am. Museum of Natural History, 1959
A new puff-bird from Colombia, Am. Museum of Natural History, 1949
Birds of the middle Sepik region, New Guinea: Results of the Am. Museum of Natural History expedition to New Guinea in 1953–1954, Am. Museum of Natural History, 1966
Notes on a Collection of Birds from Bataan, Luzon, Philippine Islands, Am. Museum of Natural History, 1950
Four new birds from the mountains of central New Guinea, Am. Museum of Natural History, 1961
A study of the coleto or bald starling (Sarcops calvus), Am. Museum of Natural History, 1949
To the land of the head-hunters: An ornithologist finds bird rarities and glimpses a dying culture in innermost New Guinea, National Geographic Society, 1955
Birds of the Victor Emanuel and Hindenburg Mountains, New Guine, Am. Museum of Natural History, 1961
Birds of the Schrader Mountain region, New Guinea: Results of the American Museum of Natural History expedition to New Guinea in 1964, Am. Museum of Natural History, 1968
Exploring New Britain's land of fire, National Geographic Society, 1961
Notes on the courtship behavior of the blue-backed manakin (Chiroxiphia pareola), Am. Museum of Natural History, 1959
The courtship behavior of Sanford's bowerbird (Archboldia sanfordi), Am. Museum of Natural History, 1959
New Guinea's Paradise of Birds, National Geographic Society, 1958
The systematics of the New Guinea manucode, Manucodia ater, Am. Museum of Natural History, 1956
Notes on some birds of northern Venezuela, Am. Museum of Natural History, 1959
A new race of Grallaria excelsa from Venezuela, Am. Museum of Natural History, 1939
Ernest Thomas Gilliard, Georg Steinbacher: Knaurs Tierreich in Farben, Droemer Knaur, 1969
Austin Loomer Rand, Ernest Thomas Gilliard: Handbook of New Guinea birds, Weidenfeld & Nicolson, 1967
Ernst Mayr, Ernest Thomas Gilliard: Birds of central New Guinea, Am. Museum of Natural History, 1954
William Henry Phelps, Ernest Thomas Gilliard: Six new birds from the Perijá Mountains of Venezuela, Am. Museum novitates; no. 1100, 1940
William Henry Phelps, Ernest Thomas Gilliard: Seventeen new birds from Venezuela, Am. Museum novitates; no. 1153, 1941
Abreviatura (zoología)
La abreviaturaGilliard se emplea para indicar a Ernest Thomas Gilliard como autoridad en la descripción y taxonomía en zoología.
Lawrence, Jenny. (1998). The passionate naturalist - ornithologist E. Thomas Gilliard. Natural History (octubre de 1998) visto 13 de marzo de 2007
Mayr, Ernst. Foreword in: “Gilliard, E. Thomas. (1969). Birds of Paradise and Bower Birds. Series: The World Naturalist. Weidenfeld & Nicolson: London”. ISBN 0-297-17030-9