Upperparts, legs, and bill are black. Underparts and forehead are white. The wings are long and narrow and the tail is deeply forked with white edged outer feathers. A black stripe running through eye to base of bill.

Nesting occurs on Eastern and Spit Islands. Breeding takes place from April through September. Birds start to breed at 6-8 years of age. Highly ritualized and vocal aerial displays are conducted over nesting area prior to settling down to lay eggs. Nesting locations change slightly from season to season. A single speckled egg is laid on ground. No nest is prepared.

Incubation period averages 30 days. Individual incubation shifts are approximately 5 days. Heat stress may cause terns to abandon eggs for short periods to drink seawater. Sooty terns are easily disturbed by human activity, and repeated disturbance may result in permanent abandonment.

Chicks are shaded by parents during hot hours and brooded only when cool. Chicks are fed every 16 hours with regurgitated food. Parents locate chicks through vocalizations, and will feed only their own. Fledging occurs at about 8 weeks. Offspring continue to be fed by parents for several weeks after fledging.