This dark eagle-owl is among the largest owls in the world and by far the largest eagle-owl found in the African rainforests. The total length of the species is 53 to 61 cm (21 to 24 in). The wing chord measured from 42 to 47.7 cm (16.5 to 18.8 in) and the tail measures 24 to 26.6 cm (9.4 to 10.5 in). A single male was reported to have weighed 1,257 g (2.771 lb), with females presumably attaining rather higher weights.
It is dark brown above overlaid with light barring. The underparts are whitish with heavy dark barring. Lighter and darker morphs are known. The light morphs have an off-white to pale tawny facial disc, with a prominent rim marked with a blackish-brown border. In the light morph, the crown and mantle are dusky brown overlaid with buffy-whitish bars. The dark morph is much darker brown above with sparse orange-buff barring, a darker facial disc and a scaly looking brownish chest. The tail and the flight feathers of all are barred with brownish colouration of light and dark. The eyes are dark brown and the feet and almost the entirety of the toes are feathered.
It is the only large, heavily built, eagle owl in Africa with such barred patterning. The Akun eagle-owl is much smaller and less barred with pale yellow eyes and bare, yellow toes. Fraser's eagle-owl is also considerably smaller, has less barring, a warmer tawny overall colouration, and bare, bluish-grey toes.
The Shelley's eagle-owl is a nocturnal bird which spends its days roosting in dense foliage, often at quite low levels in trees. Few living wild specimens have ever been studied.
Details of the species' breeding habits are not generally known. A large nestling has been observed in September in Zaire, while another in mesoptile plumage was recorded in early November. Persistent singing by the species has been heard in March.
The powerful talons of the species suggest that its preferred prey consists of medium-sized mammals and large birds. The only confirmed wild prey was a large flying squirrel. In captivity, Shelley's eagle-owls require about 110 g (3.9 oz) of food a day, mainly consisting of rodents.
This species is found in Central and Western Africa. It has been found in widely scattered locations in upper and lower Guinea, Liberia, Ghana, Cameroon, Gabon and northeastern Zaire. It is a resident of lowland, tropical rainforests and has never been collected outside densely forested areas.
Only 20 specimens of this species are known to have been collected. Further studies, especially of the life history of Shelley's eagle-owls, are needed. Based on this, it appears to be a very local and very rare bird. Due to its location in dense rainforest, it is clear that the species is threatened by any habitat loss within its native range.