These are bulky geese and their almost uniformly grey plumage, bearing rounded black spots, is unique. The tail and flight feathers are blackish and the legs are pink with black feet. The short, decurved black bill and green cere gives it a very peculiar expression.

The Cape Barren Goose is 75 to 100 cm (30 to 39 in) long, weighs 3 to 7 kg (6.6 to 15.4 lb) and has a 150 to 190 cm (59 to 75 in) wingspan; males are somewhat larger than females. This bird feeds by grazing and rarely swims. Their ability to drink salt or brackish water allows numbers of geese to remain on offshore islands all year round. They are one of the rarest of the world's geese. It is gregarious outside the breeding season, when it wanders more widely, forming small flocks. A previous decline in numbers appears to have been reversed as birds in the east at least have adapted to feeding on agricultural land. The breeding areas are grassy islands off the Australian coast, where this species nests on the ground in colonies. It bears captivity well, quite readily breeding in confinement if large enough paddocks are provided.