Subantarctic fur seals are sexually dimorphic, with adult males being 3 times heavier and 1.2 –1.3 times longer than females. In both sexes, the muzzle is straight, short, and narrow, and tapers rapidly in width and thickness to a pointed end.  The rhinarium is small.  A forehead, more abrupt in males, separates the muzzle from the elevated, but somewhat flattened, crown.  The vibrissae are very long and creamy white, and often reach well past the ears, down the neck in length.  The long ear pinnae, with naked tips, lie close to the head and are not particularly prominent.

Adult males are heavily-built; their enlarged chest and shoulders make the neck appear short.  They develop a prominent tuft, or crest of long guard hairs on top of the head above and behind the eyes and forehead.  There is no mane of longer thicker fur and no grizzling of lighter guard hairs. Adult females, young subadult males, and juveniles do not have the crest of hair on the crown.

Overall, both the fore and hind flippers are proportionately short and broad in all age classes and both sexes.  A series of vagrant animals found in South Africa had fore flippers that measured from 19–26% of body length and hind flippers that were 12–16% of body length. The fore flippers have a dark, sparse, short fur that extends beyond the wrist onto the middle of the dorsal surface of the flipper in a “V” pattern that does not reach the rounded tip.  The rest of the dorsal surface, and the palms of both fore flippers are covered with a hairless black leathery skin.  The first digit is the longest, widest and thickest, and curves posteriorly, giving the flipper a swept-back look.  Digits 2-5 are successively shorter.  There is a small opening in the skin at the end of each digit for a claw that is usually reduced to a vestigial nodule, and rarely emerges above the skin.  The claw openings are set back from the free edge of the flippers by cartilaginous rods that extend the length of each digit, and expand the size of the flippers.

The hind flippers have dark, short, sparse hair covering part of the proximal end of the flipper, and the rest of the dorsal surface, and the entire sole is covered in black leathery hairless skin.  The hind flippers are long and each digit has a cartilaginous rod that adds a flap-like extension to each toe.  The bones of the three central toes terminate at the position of the small nails that emerge through the skin on the dorsal surface, set back from the end of the flipper.  The claws of digits 1 and 5 are vestigial like the claws on the fore flippers, and may or may not emerge from small openings set back from the end of the flaps.  All of the flaps at the end of the flipper are of relatively equal length.  The first toe or hallux and the fifth toe are somewhat wider than toes 2–4. 

Subantarctic fur seals are uniquely and strikingly colored.  The back and rump of adult males is dark gray to brownish black, subadults darkening as they age.  From the chest through the muzzle, face, and area around the eyes, the pelage is continuously cream colored with yellow to orange shading possible.  The ear pinnae are mostly bare skin and dark, and attach in the dark pelage of the upperparts.  The crest of longer fur above the eyes and behind the forehead is pale and is situated in the dark fur of the crown.  Although adult males are enlarged and thick in the shoulders and neck, they do not have a mane.   

Adult females have similar coloration to males, but have less well-defined pale facial markings, which can be shaded with dull yellow orange to light reddish brown.  In both sexes, the top of the fore flippers is darker, as is the area where the flippers attach to the sides.  The underside of the abdomen is dark ginger to reddish brown.

Hybrid Subantarctic and Antarctic fur seals are known.  The few photographs available show that they share characteristics of both species.  Two adult males had crests of fur on the crown and variable amounts of pale coloration on the face, neck and chest.  One large male had a conspicuous grizzled mane, a pale muzzle, and pale rings around the eyes.  More information is needed on the appearance of hybrids.

Adult males are up to 1.8 m long and weigh 70-165 kg, and adult females are 1.19–1.52 m long and weigh 25-67 kg, with a mean of around 50 kg.  Newborns are about 60 cm long and weigh 4-4.4 kg.           

The dental formula is I 3/2, C 1/1, PC 6/5.

Subantarctic fur seals are widespread and co-occur with Antarctic and New Zealand fur seals in portions of their range.  Vagrants have been recorded on mainland South America, at the Juan Fernandez Islands, Southern Africa and Madagascar, South Australia, New Zealand and the New Zealand sub-Antarctic Islands, within the range of Juan Fernandez, South American, Cape, and Australian fur seals, and South American, Australian, and New Zealand sea lions.

Subantarctic fur seals can be differentiated from all sea lions by their distinctive coloration, wide, short, pointed muzzle, proportionately large eyes, long white vibrissae, proportionately short and wide flippers, and thick pelage.

Antarctic fur seal bulls are heavier and longer bodied with proportionately longer thinner necks.  They are more uniformly dark without the pale chest and mask; have a mane of grizzled longer fur; lack a crest of fur on the crown; have more prominent paler colored ear pinnae; proportionately smaller eyes; and proportionately longer and narrower fore and hind flippers.  Adult female Antarctic fur seals are larger but proportionately more slender; have pale coloration in the mystacial area on the muzzle, but not the extensive pale coloration on the muzzle, neck and chest; are grayer and paler above and paler and less reddish brown below; and share the same differences described for males in ear pinnae, eyes and flippers.

New Zealand and South American fur seals are more uniformly colored without the dramatic pale chest neck and face markings.  Adult males and females of both species are not as dark above and paler in the abdomen area.  They both have a long muzzle and although different from one another, an enlarged rhinarium, a mane with pale grizzling, and lack the crest of fur on the crown.  They are both also stocky, but larger overall.  Adult females of both are proportionately more slender; have pale coloration in the mystacial area on the muzzle, but not the extensive pale coloration on the muzzle, face, neck and chest of Subantarctic fur seals; are lighter gray brown on the back, and paler and less red brown below; and have a longer muzzle, and more prominent ear pinnae.

Adult male Juan Fernandez fur seals have a very long thin muzzle, distinctive bulbous rhinarium, long mane and distinctive grizzling of the crown, nape and upper neck, and overall dark coloration without the pale facial mask, muzzle, neck, and chest, of Subantarctic fur seal bulls.  Adult female Juan Fernandez fur seals share the same differences New Zealand and South American fur seal females have with Subantarctic fur seal females.

Cape and Australian fur seal bulls are very large, heavy but not stocky, with a long conspicuous mane, and more uniform pale orange brown to dark brown coloration without strongly contrasting pale areas in the face, neck and chest.  The muzzle is very long, and tapers, but only to a blunt end with a large conspicuous rhinarium.  Females are much larger than female Subantarctic fur seals and also have a longer tapering less pointed muzzle, although the rhinarium is enlarged less than in the male.  The ear pinnae in both sexes are more prominent than on Subantarctic fur seals, and both the fore and hind flippers are proportionately longer.