Adult males weigh about 100 kg and are about 180 cm long. Females are about 120 cm long and their weight is unknown. Adult males are dark greyish brown to greyish black and the tips of the guard hairs of the mane may be light. Only males are readily distinguishable from other otariids in the same range. Their heads are large and they have a long, pointed muzzle.
Females are dark grey-brown to greyish black above and paler below.
The chest and underside of the neck can be creamy grey. Breeding occurs between mid-June and July or August and because of high temperatures, both females and males prefer areas to pup and breed that have access to water or shelter. Pups are weaned between 8-11 months. Males are absent from the rookeries in the winter and it appears that all ages and sexes live at sea at different times throughout the year. Little is know about the diet of the Guadalupe fur seal but they have been observed to eat squid and lanternfish.