The adult male has a grey back and head, brick-red underparts, and white malar streaks ("moustaches").

The subalpine warbler is divided into two distinct subspecies groups, which may possibly be sufficiently diverged to qualify as two separate species (Shirihai et al.

In May 2020, the IOC world bird list the western and eastern subalpine warblers were split into two distinct species.

It is also frequently found in young cork oak (Quercus suber) forest and in dense but treeless bushy areas.

It uses bushy formations dominated by brambles (Rubus fruticosus) along sunny ravines and valley bottoms and prefers the intermediate stages of post-wildfire succession.