This gull is 38–44 cm long with a 94–105 cm wingspan. In flight, the white leading edge to the wing is a good field mark. The summer adult has a chocolate-brown head (not black, although does look black from a distance), pale grey body, black tips to the primary wing feathers, and red bill and legs. The hood is lost in winter, leaving just 2 dark spots. Immature birds have a mottled pattern of brown spots over most of the body.

The black-headed gull is a bold and opportunistic feeder. It eats insects, fish, seeds, worms, scraps, and carrion in towns, or invertebrates in ploughed fields with equal relish. It is a noisy species, especially in colonies, with a familiar "kree-ar" call.

 Like most gulls, black-headed gulls are long-lived birds, with a maximum age of at least 32.9 years recorded in the wild.