Buff-breasted Mountain-tanager is distributed in the Andes from Colombia through Ecuador to Peru. See the distribution map at xeno-canto. It is found in the understorey and borders of montane forest and woodland including Polylepis at between 2,000 and 3,500 metres. It feeds on small fruits and berries as well as insects.

The HBW and Birdlife International checklist treat the sub-species found in the Santa Marta mountains of Colombia as a species, namely Carriker's Mountain-tanager Dubusia carrikeri, based on several plumage differences such as the denser streaking on the forehead and supercilium and the extension of the buff breast up to the centre of the throat. There are also vocal differences.