The green ibis is 48–56 cm long and weighs 650–750 g; the female is smaller than the male. Breeding adults have glossy greenish-black bodies, pale green legs and bill, and grey bare facial skin patches. Juveniles are much duller, but can be distinguished from the similar glossy ibis by their bulkier shape, shorter legs and broader wings. This species, like other ibises, flies with neck outstretched. Its flight is heavy, with fewer glides and jerkier wingbeats than its relatives.
The green ibis occurs in wooded swamps and other wet forest habitats. Its nest consists of a platform of twigs placed in a tree. This species is less gregarious than its relatives and is usually seen alone or in pairs. It has been recorded as harassing sunbitterns nesting in the same tree.