The ecoregion extends from the mouth of the Paraíba do Sul River eastward along the Paraíba valley lying behind the coastal Serra do Mar, and further eastward and northward along the basin of the Paraná River and its tributaries, forming a complex mosaic with the surrounding ecoregions.

The ecoregion covers portions of the Brazilian states of Minas Gerais, São Paulo, Goiás, Mato Grosso do Sul, Paraná, Santa Catarina, and Rio Grande do Sul, the Argentine province of Misiones, and the Paraguayan departments of Alto Paraná, Amambay, Caaguazú, Caazapá, Canindeyú, Concepción, Guairá, and Itapúa.

The Cerrado lie to the north and east (in São Paulo), entwining with the Paraná-Paraíba forests in a complex mosaic.

The Alto Paraná Atlantic forests wrap around the north, east, and south of the Araucaria moist forests, which cover a higher-elevation portion of the plateau in Paraná, Santa Catarina, and northern Rio Grande do Sul states.

Protected areas include Iguazú, Caazapa, Cerro Cora, Itatiaia, Ybycui, Ñacunday, San Rafael, and Saltos del Guairá national parks, and Caetetus Ecological Station, Paulo de Faria Ecological Station, Ybera Scientific Reserve, Alto Iguazu Wilderness Nature Reserve, Urugua-í Wildlife Reserve, and Marília Ecological Station.