The dunnock is a robin-sized bird which typically measures 13.5–14 cm in length. It possesses a streaked back, somewhat resembling a small house sparrow. Like that species, the dunnock has a drab appearance which may have evolved to avoid predation. It is brownish underneath, and has a fine pointed bill. Adults have a grey head, and both sexes are similarly coloured.

The main call of the dunnock is a shrill, persistent tseep along with a high trilling note. The song is rapid, thin and tinkling. Dunnocks are a native resident to Britian and their favoured habitats include woodlands, shrubs, gardens, and hedgerows. They typically feed on the ground, often seeking out worms, invertebrats and bugs for food.

The dunnock builds a nest (predominantly from twigs and moss and lined with soft materials such as wool or feathers), low in a bush or conifer tree, where adults typically lay three to five unspotted blue eggs. Females are often polyandrous, breeding with two or more males at once. Males sometimes share a territory and exhibit a strict dominance hierarchy. Nevertheless, this social dominance is not translated into benefits to the alpha male in terms of reproduction.