Subantarctic Fur Seals are sexually dimorphic, with adult males being up to 1.8 m long and weighing 70-165 kg; adult females are 1.19–1.52 m long and weigh 25-67 kg, with a mean of around 50 kg. Newborns weigh 4-4.4 kg (Laws 1993). Females attain maturity at 5 years of age (Bester 1995). Gestation lasts 51 weeks. Longevity is unknown (Reijnders et al. 1993).

Subantarctic Fur Seals are polygynous; males defend territories with vocal and postural displays and fighting (Bester 1981, Kerley 1983). They prefer rough rocky or boulder beaches with sources of shade or exposure to prevailing winds (Bester 1982). Pups are born from late October to early January, with a peak in mid-December. Females give birth within 6 days of arriving at the colony with oestrous and mating occurring 8-12 days later. Females spend the time between the births of their pups and oestrous, with their newborn before mating and departing for the first of a series of foraging trips they will make before weaning their pup at approximately 11 months of age (Bester 1981, Kerley 1983). Trip durations of mothers increase over the course of lactation from 6-10 days to 23-28 days (Georges and Guinet 2000, Kirkman et al. 2002). Dives become deeper and slightly longer over the summer, starting at a mean depth of 16.6 m and increasing to 19 m. Dives are seldom deeper than 100 m or longer than 4 minutes (Georges et al. 2000).

Subantarctic Fur Seals are sympatric with other species of fur seals at three sites. Hybridization with Antarctic Fur Seals occurs at the Prince Edward Islands (Hofmeyr et al. 2006a) and the Îles Crozet (Guinet et al. 1994), and with both Antarctic Fur Seals and New Zealand Fur Seals at Macquarie Island (Goldsworthy et al. 1999).

Subantarctic Fur Seals are opportunistic and pelagic foragers. They feed on myctophid and notothenid fish, cephalopods, and small numbers of crustaceans at the Prince Edward Islands (Klages and Bester 1998) and at Macquarie Island (Robinson et al. 2002). At Amsterdam Island they are know to take Rockhopper Penguins (Paulian 1964).