Carnaby's black cockatoo is 53–58 cm (21–23 in) in length with a 110 cm (43 in) 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 2.5–3 cm (0.98–1.18 in) 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.

The adult male has a dark grey beak and pink eye-rings.
The adult female has a bone-coloured beak, grey eye-rings and ear patches that are whiter and more distinctive than those of the male.
The feathers of its underparts and underwing coverts have larger white margins than those of the male, leading to a more barred or scalloped pattern to its plumage.
Its legs and feet are a little lighter than those of the male.
Moulting appears to take place in stages in late summer—some time between January or February and April or May, and is poorly understood.

Juveniles have a bone-coloured beak, grey eye-rings, and less white in the tail feathers.
They can also be distinguished by their constant begging calls.
It is not possible to tell the sexes apart until the male's bill begins to darken.
This begins when the male is around one year old, and is complete some time after two years of age.
Carnaby's black cockatoo is 53–58 cm (21–23 in) in length with a 110 cm (43 in) 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 2.5–3 cm (0.98–1.18 in) 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.
The adult male has a dark grey beak and pink eye-rings. The adult female has a bone-coloured beak, grey eye-rings and ear patches that are whiter and more distinctive than those of the male. The feathers of its underparts and underwing coverts have larger white margins than those of the male, leading to a more barred or scalloped pattern to its plumage. Its legs and feet are a little lighter than those of the male. Moulting appears to take place in stages in late summer—some time between January or February and April or May, and is poorly understood.
Juveniles have a bone-coloured beak, grey eye-rings, and less white in the tail feathers. They can also be distinguished by their constant begging calls. It is not possible to tell the sexes apart until the male's bill begins to darken. This begins when the male is around one year old, and is complete some time after two years of age.
Carnaby's black cockatoo