[3][4] The long-billed wren is 19 to 21.5 cm (7.5 to 8.5 in) long and weighs 20 to 21 g (0.71 to 0.74 oz).

The crown and nape of adults of the nominate subspecies are rich dark brown that becomes progressively more reddish to the rump; the lower back has obscure bars.

[4] C. l. bahiae is the more northerly subspecies of long-billed wren; it is found in the "bulge" of eastern Brazil from Piauí south to Minas Gerais and east to the Atlantic coast.

C. l. longirostris is found in a narrower coastal band from Bahia south to eastern Santa Catarina.

[4] The long-billed wren's diet has not been studied, and its foraging habits are not well known.