Southern Elephant Seals are the largest of all pinnipeds with adult males reaching masses of two to four tons and lengths of up to 4.5 m. They show considerable sexual dimorphism, with adult females only reaching masses of 400-900 kg and average lengths of 2.8 m. Newborn pups weigh between 40 and 46 kg (Laws 1993). Females first haul out to pup at ages of three to six years, and males typically breed for the first time at six to ten years of age (Laws 1956, Carrick et al. 1962a, Jones 1981, McCann 1981, Pistorius et al. 2001, Kirkman et al. 2004). At Marion Island, less than 5% of females survived beyond 13 years of age, and less than 5% of males beyond 10 years of age (de Bruyn 2009). Longevity of 23 years has been recorded for adult females at Macquarie Island (Hindell and Little 1988).

Southern Elephant Seals undergo an annual double migration between foraging grounds and isolated haulout sites, at which they are born and where they breed in the austral spring, moult in the austral summer, and as immatures haulout in the winter (Bartholomew and Hubbs 1960, Carrick et al. 1962b, Hindell and Burton 1988). Southern Elephant Seals are predominantly marine. Adult females spend more than 85% of each year at sea while adult males spend less than 80% (Carrick et al. 1962a, Hindell and Burton 1988, McIntyre et al. 2010). Their foraging grounds may be located over 5,000 km from their terrestrial haulout sites (Bester and Pansegrouw 1992, Jonker and Bester 1998, Campagna et al. 1999, Bailleul et al. 2007).

Southern Elephant Seals spend most of their at-sea time foraging in association with frontal systems, currents and shifting marginal ice-edge zones. Studies of foraging sites suggest that they are sensitive to fine-scale variation in bathymetry and ocean properties (sea-ice concentration and sea temperature profiles) (Bailleul et al. 2007, Biuw et al. 2010). Southern Elephant Seals are prodigious divers. Dive depth and duration vary during the year and between the sexes, but mostly range from 200 to 700 m deep and from 20 to just over 30 minutes in duration (Biuw et al. 2010, McIntyre et al. 2010). Both sexes spend over 65% of their lives below 100 m. The maximum record dive depth is 2,133 m for an adult male (McIntyre et al. 2010).

The diet varies between populations and seasons. It consist primarily of myctophid and notothenid fish and squid (Brown et al. 1999, Piatkowski et al. 2002, Bradshaw et al. 2003, van den Hoff et al. 2003, Cherel et al. 2008, Newland et al. 2011).

Four types of terrestrial periods are experienced over the course of their lives: the breeding, moult and winter haulouts, and the natal terrestrial period. The mating system is mate-defense polygyny. Breeding seasons are highly synchronized (Carrick et al. 1962b, Laws 1956, McCann 1981, Bonner 1989). Adult females spend approximately a month ashore during the breeding season, while adult males may spend one to three months ashore. During this time adult females will haul out in large aggregations that may contain up to a thousand animals (Carrick et al. 1962a, Bonner 1989). Some three to seven days after females come ashore they give birth to a single pup, which they will suckle for some three weeks. Mating takes place shortly before the pup is weaned and the adult female returns to the sea a few days later. Breeding aggregations are ephemeral, and do not last beyond the breeding season. Access to all females in one breeding aggregation is defended by a dominant adult male. In larger breeding aggregations, subdominant males also gain access to females (Laws 1956, Carrick et al. 1962a, McCann 1981).

Killer Whales are the primary predators of Southern Elephant Seals (Reisinger et al. 2011) but Leopard Seals are also known to take pups (Gwyn 1953).

Southern Elephant Seals have a nearly circumpolar distribution in the Southern Ocean. While most haulout sites are on Subantarctic and Antarctic islands, a number of animals haul out regularly at sites on the coasts of southern Argentina and Chile (Campagna and Lewis 1992) and Antarctica (Bester 1988, Heimark and Heimark 1986, Murray 1981). They forage at sea between about 40° south and the Antarctic Continent. Occasional vagrants have been recorded on the coasts of northern South America (Alava and Carvajal 2005, De Moura et al. 2010), southern Africa (Kettlewell and Rand 1955, Oosthuizen et al. 1988), Australia and New Zealand (Mills et al. 1977, Taylor and Taylor 1989). The most distant vagrant was recorded at Oman on the Arabian Peninsula, some 9,000 km from the nearest possible point of origin (Johnson 1990).