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) [XC466221]
by Ricardo Gagliardi from Ilha Barnab\u00e9, Santos, S\u00e3o Paulo State, Brazil (song)
Spix's Spinetail (Synallaxis) [XC531366]
by Marcelo H\u00fcbel from Fazenda Monte Azul, Cachoeiras de Macacu, Rio de Janeiro, Brazil (call, 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.