The adult kelp gull is white with black upperparts and wings. The bill is bright yellow with a red spot near the tip and the eyes are dark brown with an orange eye ring. The feet are a whitish-yellow.
The immature kelp gull is initially a mottled dark brown with a paler barred rump. It can be mistaken for a skua, but lacks the white patches at the primary bases. It has an all yellow bill.
In South Africa the kelp gull breeds in spring and early summer at Wolfgat Nature Reserve (Swartklip) and Rondevlei. They usually breed on off-shore islands but nests are sometimes found on unfrequented cliffs.
The nest is a scrape in the soil and lined with grass, feathers or twigs. Two to three eggs varying in colour from light green to turquoise or ochre with dark markings are laid.