False killer whales are usually 5 to 6 metres long. They are more slender and streamlined, and lack the striking black and white body pattern of the killer whales.

The head has a narrow profile and the lower jaw ends well before the tip of the rounded rostrum. The flippers are pointed and have a distinct 'elbow' in the middle, and the dorsal fin, although much smaller than that of the killer whales, is still prominent and is distinctly hooked with a rounded tip.

There are 8 to 11 pairs of robust teeth in each jaw. Most specimens are completely black but some may have a blaze of grey in the shape of an anchor from the tip of the lower jaw along the throat towards the navel and on the underside of the flippers.