Coprosma chathamica is a fast-growing canopy tree reaching a height of 15 m in its natural habitat. It is endemic to the Chatham Islands where it grows in scattered, moist, self-draining sites in the coastal and inland forest areas.

The fleshy, glossy, dark green adult leaves are >4 cm long and are in pairs. They have faint veins which have a small pit at some of their junctions with the main rib. Young trees have very large juvenile leaves >12cm long and they usually have distinctly hairy margins. Both female and male flowers are produced during early summer. These are followed by 9mm, yellowish red drupes.