Pied shags mainly inhabit coastal habitats about much of New Zealand. Adults have the crown, back of the neck, mantle, rump, wings, thighs and tail black, although on close inspection the upper wing coverts are grey-black with a thin black border. The face, throat, sides of neck and underparts are white. The long, hooked beak is grey, the iris is green, and legs and feet black. On breeding adults, the skin in front of the eye is yellow, at the base of beak is pink or pink-red, and the eye-ring is blue. Non-breeding adults have paler skin colours than breeders. The upperparts of juveniles and immatures have dark and pale brown tones. Their underparts are white but with varying amounts of brown mottling, from almost entirely brown to little at all. The skin in front of eye is pale yellow, at the base of the beak is grey – pale pink, and eye-ring is grey.

Voice: generally silent away from nesting colonies, but quite vocal at colonies during pair formation, nest building and when one of a pair returns to nest during incubation. Females give wheezy haa calls, while males give a variety of loud calls, that may be repeated several times, and that sound like aark, kerlick and whee-eh-eh-eh.

Similar species: the pied morph of the little shag is much smaller and has a short stubby yellow beak. Both the king shag and pied morph of the Stewart Island shag have black heads with white throats, patches of white feathers on the upper wings, and pink feet. Juveniles and immatures of black shag can be difficult to distinguish from the similar-sized juveniles and immatures of pied shag. Both can have underparts from nearly all brown to nearly all white. Juvenile black shags have dark heads and upper throat, and have extensive yellowish facial skin about base of the beak, whereas the yellow is only in front of the eye on the pied shag.