Green Thorntail is resident from Costa Rica south to western Ecuador. In Costa Rica, the thorntail is restricted to the Caribbean slope, on the Cordillera Central and Cordillera Talamanca (Stiles and Skutch 1989), but most records in Panama are from the Pacific slope, although it "likely occurs at similar elevations on the Caribbean slope as well" (Ridgely and Gwynne 1989). Green Thorntail also occurs along the Pacific slope of western Colombia and western Ecuador, south to El Oro and western Loja (Hilty and Brown 1986, Ridgely and Greenfield 2001a).
At least in Costa Rica, Green Thorntail undergoes elevational movements; the primary elevational range is 700-1400 m, but it descends to 60 m in the early wet season (June-August) (Stiles and Skutch 1989; see also Stiles 1980). Elsewhere, it is reported at "mostly" 600-1200 m in Panama (Ridgely and Gwynne 1989); from the lowlands up to 1000 m (once to 1400 m) in Colombia (Hilty and Brown 1986); and at 300-1000 m in Ecuador, although there are records to as low as 70 m, suggesting that it locally is resident to lower elevations or that, as in Costa Rica, there are seasonal elevational movements (Ridgely and Greenfield 2001a).