The cliff swallow's average body length is , they have short legs and small bills with relatively long pointed wings. Adult cliff swallows have an overall dark brownish plumage covering both their back and wings, they have a characteristic white forehead, rich red coloured cheeks with a dark throat, basic white underparts and a buffy-coloured rump. In good lighting occasions, their crowns and mantle feathers are iridescent. The Northern population is slightly larger in body size from the Mexican cliff swallow population and differ in facial markings, where the Mexican population have a chocolate brown patch on their forehead.