The martial eagle is a very large eagle, with an average length of 78–96 cm (31–38 in), weight of 3–6.2 kg (6.6–13.7 lb) and a wingspan of 188–260 cm (6 ft 2 in–8 ft 6 in).[2][3][4] Its total length – in comparison to its wingspan – is restricted by its very short tail. Among standard measurements, the wing chord is 56–67.5 cm (22.0–26.6 in), the tail is 27.2–32 cm (10.7–12.6 in), the tarsus is 9.7–13 cm (3.8–5.1 in).[2] This is the largest eagle in Africa and is the fifth heaviest (on average) eagle in the world.[2][4]

The adult’s plumage consists of dark grey-brown coloration on the upperparts, head and upper chest, with slightly lighter edging to these feathers. The body underparts are white with blackish-brown spotting. The underwing coverts are brown, with pale flight feathers being streaked with black. The female is usually larger and more spotted than the male. The immature is paler above, often whitish on the head and chest, and has less spotted underparts. It reaches adult plumage in its seventh year. Martial eagles have a short erectile crest, which is often not prominent. It often perches in a quite upright position, with its long wings completely covering the tail. The bill, at 5.5 cm (2.2 in), is strong and the legs are feathered to the heavy, powerful feet.[2] There are few serious identification challenges for the species. The black-chested snake eagle is smaller, with a relatively more prominent head and white lining the flight feathers. The crowned eagle, which also regularly perches in an erect position, has distinctly shorter wings and a distinctly longer tail and, though its plumage is fairly variable, it is more scaled on the back and it has distinctive barring on the underparts and the wings. More so than any other African eagle, the martial eagle is often seen only in flight.[2]

Martial eagles have been noted as remarkable for their extremely keen eyesight (3.0–3.6 times human acuity). Due to this power, they can spot potential prey from a very great distance.