The Ash-breasted Sierra-finch is distributed in the Andes of Ecuador, Peru, western Bolivia, northern Chile and western Argentina south to Mendoza. There is a disjunct population on the Serra de Córdoba, Argentina.

It is the smallest sierra-finch and is common and conspicuous being found in large flocks in the non-breeding season. Presumably the fact that it is so common gave rise to both its specific and its Chilean name.

Although Fjeldså & Krabbe say that sexes are alike, most authorities mention that the female is lightly streaked on the throat and breast as can be seen on the birds in photos 3 and 4.