Adults of the nominate subspecies S. a. azarae have a brownish gray face with a slightly paler supercilium.

Their iris is reddish brown to chestnut, their maxilla black to dark gray, their mandible gray or blue-gray (sometimes with a blackish base or tip), and their legs and feet olive-gray to grayish green.

[3] The other subspecies of Azara's spinetail differ from the nominate and each other thus:[3][6][7][8] The subspecies of Azara's spinetail are found thus:[3] Azara's spinetail inhabits a variety of semi-open landscapes both humid and drier, including the edges of montane evergreen forest, secondary forest, the edges of cloudforest and elfin forest, bushy pastures and roadsides, riparian thickets, and in Argentina semi-deciduous and deciduous woodlands.

[3] Azara's spinetail feeds on arthropods; its diet also includes small seeds.

It gleans prey from foliage, small branches, and occasionally dead leaves.

Its nest is a longish mass of sticks with a horizontal or upward entrance tube; the inner chamber is lined with soft plant material and sometimes includes shed snake skin.

The incubation period, time to fledging, and details of parental care are not known.

Azara's spinetail is quite vocal, repeating for minutes at a time a sharp "ket-kwééék", "pip-squeak", or "ka-kweeék".