Carnaby's black cockatoo is in length with a wingspan, and weighs 520–790 grams. It is mostly greyish black, with narrow light grey scalloping produced by narrow off white margins at the tips of dark feathers. The scalloping is more prominent on the neck. It has a crest of long feathers on its head that form a short crest that can be raised and lowered, and a prominent off-white patch of feathers on its cheek. Its lateral tail feathers are white with black tips, and the central tail feathers all black. The irises are dark brown and the legs brown-grey. Its beak is shorter and broader than that of the closely related and similar Baudin's black cockatoo; the two are often difficult to distinguish in the field.