Great Dusky Swift occurs in east central South America, in Bolivia, Brazil, Paraguay, and Argentina. In Bolivia it is reported only from northeastern Santa Cruz (Whitney et al. 1994, Bates and Parker 1998), where "seemingly ideal breeding habit" is present (Whitney et al. 1994), but breeding remains unconfirmed from this region. This swift breeds in southeastern Paraguay (Hayes 1995, Guyra Paraguay 2004) and in northeastern Argentina in Missiones. In Brazil it occurs from Mato Grosso east to southern Pará, and south to Rio Grande do Sul (Sick 1993, Pacheco and Olmos 2005, Oliveira 2011).
Described as being locally abundant in Brazil, but scarce in Paraguay and other areas (Hayes and Scharf 1995).
Hilty and Brown (1986) suggested that Great Dusky Swift might be a trans-Amazonian migrant, based on undocumented sight records, thought to be of this species, from northeastern Peru. There is no confirmation, however, that Great Dusky Swift does in occur in Peru, and now it usually is considered to be resident across its range (Chantler 2000).