This skulking passerine bird is typically found in wet lowland grassland, open woodland, scrub and sometimes gardens. The Plain Prinia builds its nest in a shrub or tall grass and lays 3-6 eggs. (The Tawny-flanked Prinia nests in herbage and lays 2–4 eggs.)

These 13–14 cm long warblers have short rounded wings, a longish tail, strong legs and a short black bill. In breeding plumage, adults are grey-brown above, with a short white supercilium and rufous fringes on the closed wings. Underparts are whitish-buff. The sexes are identical.

In winter, the upperparts are a warmer brown, and the underparts more buff. The tail is longer than in summer. There are a number of races differing in plumage shade. The endemic race in Sri Lanka retains summer plumage, including the shorter tail, all year round.

Like most warblers, the Plain Prinia is insectivorous. The song is a repetitive tlee-tlee-tlee.