Adult common gulls are 40–46 cm long, noticeably smaller than the herring gull and slightly smaller than the ring-billed gull. It is further distinguished from the ring-billed gull by its shorter bill. The body is grey above and white below. The legs are yellow in breeding season, becoming duller in the winter. In winter, the head is streaked grey and the bill often has a poorly defined blackish band near the tip, which is sometimes sufficiently obvious to cause confusion with ring-billed gull.

They have black wingtips with large white "mirrors" on the outer primaries. Young birds have scaly black-brown upperparts and a neat wing pattern, and pink legs which become greyish in the second year before tuning yellow. You can tell the difference from a herring gull by the lack of red marking on its bill.

The common gull will breed near water or in marshes, making a lined nest either on the ground or in a small tree. The colony size varies from 2 to 320 or even more pairs. Usually two or three eggs are laid and will hatch 24–26 days later.