Colouration is uniform dark brown to sooty black; juveniles are generally darker than adults; underwing feathers are two-tone (flight feathers slightly paler); adults may have an evident dark stripe below the eye.

When attempting to identify a flying raptor Debus & Davies[3] recommend concentrating on the bird's silhouette (including shape of wings and proportions), flight style and vocalisations, rather than on details of colouration.

The two species differ in the relative length of exposed tarsi (the lower, visible half of the bird's leg) compared with thigh feathers, flight style, wing attitude, and bold underwing barring and tail barring (which appear on the brown falcon only).

[10] The black falcon is widely distributed across mainland Australia, except densely forested areas.

The species is only occasionally seen in the southern interior of WA and is sparse in coastal areas of south eastern Australia.

While resting the bird's wing tips are shorter than the tail and legs appear short.

They will sometimes tail chase other birds over long distances, and less often engage in a Peregrine-like vertical stoop when hunting.

[13] The black falcon's diet primarily consists of bird species, from finch to cockatoo size but they have also been observed feeding on small mammals (i.e. rabbits, mice and rats), insects and carrion.

[2][6] Avian prey species include: Debus & Zuccon also observed the black falcon hunting turquoise parrot (Neophema pulchella) and apostlebird (Struthidea cinerea), but on these occasions the attacks were unsuccessful.

[4] It appears there may be interspecific competition for nest sites between the black falcon and other raptors and corvids.

[14] Nest sites may be a limiting factor for black falcons, specifically where there has large-scale vegetation clearing, such as occurred in the sheep-wheat belt of NSW.

[2] During breeding season males perform courtship displays such as horizontal figure eights around the nest.

[2] Declining numbers of black falcons is a growing concern, with two states (Victoria and New South Wales) already having listed the species as vulnerable.

Several authors have pointed out that population and other ecological data on the species is deficient, and addressing this issue should be a major priority for managers in the future.

Disturbance of nest sites and harassment by other birds (including cockatoos) also appears to impact the falcon's breeding success.

[2][3] The Office of Environment and Heritage (NSW Government) has identified eight priority actions that aim to help recover the species.