It is a distinctive subspecies of the Eurasian wren endemic to the islands of the isolated St Kilda archipelago, in the Atlantic Ocean 64 kilometres (40 mi) west of the Outer Hebrides, Scotland.

The St Kilda wren is distinguished from the mainland form by its larger size and heavier barring, as well as its generally greyer and less rufous colouration.

It differs from other Scottish island sub-species by its heavy barring, long and strong bill, and its greyer and paler plumage.

In the breeding season it is largely found on the cliffs and steep rocky slopes with thick vegetation, but also around old buildings.

Most birds breed in crevices and holes on cliffs concealed behind grasses and dead thrift.