Bangladesh, Bhutan, Brunei Darussalam, Cambodia, China (mainland), India, Indonesia, Laos, Malaysia, Myanmar, Nepal, Philippines (B), Singapore (B), Thailand, Vietnam.
Vagrant to Hong Kong (China).
Nepal, north-eastern India (east to Arunachal Pradesh, south to Mizoram, Manipur, Nagaland) and Bangladesh to southern China (western Yunnan, Hainan) south through Indochina and Malay Peninsula to Sumatra and surrounding islands, Deli I (south of western Java), Borneo and western Philippines (Mindoro, Palawan, Balabac).
 
Population
Estimated population is unknown (2010).
Thick-billed Green Pigeon (Treron curvirostra) [XC360101]
by Peter Boesman from Klias Forest Reserve, Sabah, Borneo, Malaysia (song)
Thick-billed Green Pigeon (Treron curvirostra) [XC498463]
by Frank Lambert from North Siberut, Kepulauan Mentawai, West Sumatra, Indonesia (song)
Subspecies
Closely related to Sri Lanka Green-pigeon (Treron pompadora). Possibly best considered as forming a superspecies with Grey-cheeked Green-pigeon (Treron griseicauda), Flores Green-pigeon (Treron floris), Sumba Green-pigeon (Treron teysmannii) and Timor Green-pigeon (Treron psittaceus), though all have been considered conspecific. Also, considered conspecific rarely, with Sri Lanka Green-pigeon (Treron pompadora). Numerous subspecies have been described, based on minor differences of questionable significance.
The following 9 subspecies are recognised:
nipalensis (Hodgson, 1836) - Central Nepal and north-eastern India through Myanmar to southern Indochina.