Native to the southern regions of South America, the Greater Rhea is endemic to Argentina, Bolivia, Brazil, Paraguay, and Uruguay. In Brazil, it occurs northeast to Maranhão, and formerly to Ceará and Rio Grande do Sul (Sick 1993). In occurs only in the easternmost departments of Bolivia, in Beni, Santa Cruz, and Tarija (Hennessey et al. 2003). The southern distributional limit is in northeastern Río Negro, Argentina (Blake 1977).

The elevational distribution of the Greater Rhea is from the lowlands up to 1200 m (Parker et al. 1996).

No species of rhea occurs outside South America.

Greater Rheas prefer spacious open plains with low vegetation (under 50 cm) in which they can nest with some degree of cover and still be able run and feed while remaining effectively vigilant.  The Greater Rhea lives in a variety of South American savanna habitats, especially in the tall grass steppe pampas, areas of the Chaco, and the dense grassland of Brazil's campos, interspersed with scrub and scattered trees bordering forests and farmlands.

Such habitats tend to be dry, and rheas prefer to breed near rivers, lakes, and swamps.

The Greater Rhea formerly was more widespread in northeastern Brazil, occurring commonly ("flocks of 20-30") in Ceará and Rio Grande do Norte until the early 1900s, but now is exterminated from the region (Sick 1993).

Rheas have left fossils dating back to the Eocene period (~40 million years ago). They probably first appeared near the start of the Tertiary, originating in South America, making them some of this continent's oldest birds.