This is a medium to large species at 43 cm. Its head and body are purple-black, the wings are maroon above and black below, and the long tail is dark green. The bill is a distinctive light green. Sexes are similar, but juveniles are duller and streaked.
This species is somewhat smaller and less contrasted than the more widespread greater coucal. Despite its size and distinctive call, this is a difficult species to see because of the dense habitat in which it lives and its retiring nature.
This coucal has a small and declining population as a result of the forest destruction.
- Wijesinghe, Martin (1999). "Nesting of Green-billed Coucals Centropus chlororhynchos in Sinharaja, Sri Lanka" (PDF). Forktail. 15: 43–45.
- Anonymous (1998). "Vernacular Names of the Birds of the Indian Subcontinent" (PDF). Buceros. 3 (1): 53–109. Archived from the original (PDF) on 1 April 2010.
- BirdLife International (2004). "Centropus chlororhynchus". IUCN Red List of Threatened Species. Version 2006. International Union for Conservation of Nature. Retrieved 11 May 2006. Database entry includes a range map, a brief justification of why this species is vulnerable, and the criteria used