Black Swans are primarily black-feathered birds, with white flight feathers. The bill is bright red, with a pale bar and tip; and legs and feet are greyish-black. Cobs (males) are slightly larger than pens (females), with a longer and straighter bill. Cygnets (immature birds) are a greyish-brown with pale-edged feathers.[4]

A mature Black Swan measures between 110 and 142 cm (43-56 in) in length and weighs 3.7–9 kg (8.1-20 lbs). Its wing span is between 1.6 and 2 metres (5.3-6.5 ft).[4][5] The neck is long (relatively the longest neck among the swans) and curved in an "S"-shape.

The Black Swan utters a musical and far reaching bugle-like sound, called either on the water or in flight, as well as a range of softer crooning notes. It can also whistle, especially when disturbed while breeding and nesting.[4][6]

The Black Swan is unlike any other Australian bird, although in poor light and at long range it may be confused with a Magpie Goose in flight. However, the Black Swan can be distinguished by its much longer neck and slower wing beat.[7]