Eastern Paraguay, south-eastern Brazil (southern from south-eastern Bahia and southern Espírito Santo), north-eastern Argentina (south to eastern Santa Fe, Entre Ríos and northern Buenos Aires) and Uruguay.
 
Population
Estimated population is unknown (2010).
Spix's Spinetail (Synallaxis) [XC305947]
by Jerome Fischer from Dique do Furadinho, Cubat\u00e3o, S\u00e3o Paulo, Brazil (alarm call)
Spix's Spinetail (Synallaxis) [XC303213]
by Roney Souza from Caratinga, Caratinga, Minas Gerais, Brazil (song)
Subspecies
No subspecies.
Close relationship to Pale-breasted Spinetail (Synallaxis albescens) and Dark-breasted Spinetail (Synallaxis albigularis) suggested by plumage and vocal similarities. In the past was considered conspecific with Cinereous-breasted Spinetail (Synallaxis hypospodia). The two are thought to be possibly sister-species by some authors, but others consider them not closely related because of differences in tail morphology, throat pattern and voice.