The Hector’s dolphin is much smaller than other dolphins seen in New Zealand waters. An adult Hector’s dolphin grows to a length of 1.2 to 1.4 metres, compared with 4 metres for the bottlenose, 3.4 metres for the striped dolphins and the Dusky dolphins 2 metres. Also, the Hector’s is a little rounder than other New Zealand dolphins.

The Hector’s does not have a bottle-shaped snout. The forehead of the Hector’s slopes down to the tip, so it does not create a protruding beak like the bottlenose dolphin.

It has a small, rounded dorsal fin – all other species of dolphin found in New Zealand waters have crescent shaped fins that are more pointed than the Hector's.

The colour scheme of the Hector’s dolphin is well defined with areas of grey, black and white.

The sides of the head, the flippers, dorsal fin and the tail are all black. The belly is white except for a small area between the flippers. There is also a distinctive finger-like swoosh of white that extends from the belly, along the flanks towards the tail. The rest of the body is grey.