From Veracruz, northern Oaxaca, Tabasco, Chiapas and southern Quintana Roo (Peters 1913) south on Gulf-Caribbean slope of Central America to Honduras, in Nicaragua (both slopes), Costa Rica (Caribbean slope, central plateau, and Pacific slope in Golfo Dulce region) and Panama (both slopes but more widespread on Caribbean slope); and in South America from Colombia, Venezuela, Trinidad and Tobago and the Guianas south, west of Andes to western Ecuador and east of Andes to eastern Peru, Bolivia, eastern Paraguay, extreme northeastern. Argentina, and central and eastern Brazil (Peters 1913, American Ornithologists' Union 1998, Stiles and Skutch 1989, Howell and Webb 1995).
The elevational distribution of the Giant Cowbird varies across its range. In Mexico, it occurs up to 750 m (Howell and Webb 1995); in Costa Rica, up to 1700 m (Stiles and Skutch 1989, Skutch 1996); up to 2200 m in Colombia (Hilty and Brown 1986, Skutch 1996); to 1700 m in Venezuela (Hilty 2003); to 2000 m in Ecuador (Ridgely and Greenfield 2001); and to 1200 m (locally) in Peru (Schulenberg et al. 2007).