[2] Cetti's warbler was described in 1820 by the Dutch zoologist Coenraad Jacob Temminck from specimens collected by Alberto della Marmora in Sardinia.

The upperparts are a rich chestnut or dark reddish-brown; the throat and breast are pale grey.

[citation needed] The sexes have similar plumage, but males are 26% to 32% heavier than females with a wing-length 11.2% to 13% longer.

[9][10] Cetti's warbler is unusual among passerine birds in having ten tail feathers (rectrices) rather than the usual twelve.

[7] Their song is distinct, comes in loud bursts, and has a unique structure that allows the birds to avoid mating with other species.

[12] Cetti's warbler usually inhabits damp areas including ponds, lakes, marshes and rivers.

[17] The UK population of Cetti's warblers fell by over a third between 1984 and 1986 following a severe winter, but rebounded rapidly thereafter.

Populations continue to grow; by 2016 there were over 3,400 territorial males,[8] distributed throughout most of England and Wales, with the first breeding in Scotland in 2023.

The untidy cup shaped nest is made from leaves and stems and is lined with feathers, hair and other finer material.