The dusky dolphin is a medium-sized dolphin, ranging from 1.8m to 2m in length. It has virtually no beak, as the head slopes evenly down from the blowhole to the tip of the snout. The tip of the dorsal fin is rather blunt and is not markedly hooked. A dusky dolphin has a bluish-black tail and back. A dark band runs diagonally across the flanks from below the dorsal fin towards the vent and along the tailstock. The underside of the body is white, and whitish-grey color extends over the flanks. The tips of the snout and lower jaw are dark. A grey area extends from the eye down to the flipper. Two diagonal whitish streaks run forward from tail up past the base of dorsal fin (Baker 1990).

There are 24-36 pairs of small, pointed teeth about 3mm in diameter in each jaws. The upper jaw ususally has 2 less teeth than the lower (Dawson 1985).