This is the single species of the genus Callorhinus. Size and weights of this species are remarkably different depending on sex. Fully mature males have a head and body length of 213 cm and weights from 181-272 kg. Mature females are about 142 cm long and weigh between 42-50 kg. Coloration of adult males is dark gray to brown above, grayish shoulders and foreneck and a short mane. The underparts and flippers are reddish brown. Adult females and immature males are grayish brown above, reddish brown underparts and a pale area on the chest. There is a heavy underfur in both sexes and the pelage stops at an abrupt line at the wrist on the flippers.

Northern Fur Seals eat a mixture of pelagic fish and squid. C. ursinus spends most of its life at sea, coming ashore primarily to breed. This accounts for 60-70 days per year and occur on a few tiny islands found within the vast oceanic range of the Northern fur seal. The greatest migratory distances traveled by any pinniped are traveled by C. ursinus. Depending on sex and age, the Northern fur seal leaves its breeding island at various times. In the northern part of its range in the Pribilof Islands, C. ursinus migrates to wintering areas in the Aleutian Islands and on to the Gulf of Alaska. While at sea, Northern Fur Seals are active mainly at night and morning and evening hours, sleeping on one side during the middle of the day. Activity at the rookeries, however, continues around the clock. C. ursinus is an excellent swimmer and diver, traveling as fast as 24km/hr for short distances.

Females make their first trip from the birthing grounds about 7 days after delivering their young. These feeding trips can last from 4-9 days and are punctuated by trips back to the rookery to nurse their babies for 2 days. Males may remain at the rookery during breeding season for up to 2 months living on fat reserves. In the Pribilofs, the breeding season begins in early June, when the males arrive at the Islands. When the females arrive in mid June, they congregate in groups of between 1-100, more often an average of 40 are present. There is no harem formation, though, and males have no control over the movements of the females. No social bonds other than those between mother and suckling young seem to be formed. About 2 days after the females arrive on shore they give birth. Mating takes place 6 days later and the blastocyst enters the uterus where implantation is delayed for 3.5-4 months. Gestation is about 11.75 months. There is usually a single offspring, born between June 20 and July 20. Rarely, but more frequently recorded in C. ursinus than any other otariid, twins are born. Average sizes of babies at birth are 66 cm long and 5.4 kg. for males and 63 cm long and 4.5 kg for females. Newborns have a coarse black coat which they shed at about 8 weeks. The new coat is steel gray above and creamy white below. Though they are capable of swimming at birth, the pups remain at the rookery for about a month. They are weaned after 3-4 months and there is no apparent contact between mother and young thereafter. Sexual maturity in females is reached at 3-7 years, and they are able to give birth once a year until about age 23. Sexual maturity in males is achieved at 5-6 years of age, but they cannot maintain a breeding territory until 10-12 years of age.

Because of their thick underfur, C. ursinus' pelt is one of the most valuable of any pinniped. Because of this, the Pribilof Island population was over hunted. Harvesting restrictions were implemented from 1835 to 1867, allowing only immature males to be taken. After the purchase of Alaska by the United States, the restrictions were lifted and the population suffered greatly. The species is still in crisis today.

They are found in the North Pacific coastal regions in Canada, China (vagrant to Shangdong), Japan, Mexico (coasts of Baja California), Russia (Okhotsk and Bering Seas, Commander and Pribilof Isls), USA (Alaska, Washington, Oregon, S California).