The Weddell Sea is part of the Southern Ocean and contains the Weddell Gyre. Its land boundaries are defined by the bay formed from the coasts of Coats Land and the Antarctic Peninsula. The easternmost point is Cape Norvegia at Princess Martha Coast, Queen Maud Land. To the east of Cape Norvegia is the King Haakon VII Sea. Much of the southern part of the sea is covered by a permanent, massive ice shelf field, the Filchner-Ronne Ice Shelf.

The sea is contained within the two overlapping Antarctic territorial claims of Argentine Antarctica, the British Antarctic Territory, and also resides partially within the Antarctic Chilean Territory. At its widest the sea is around 2,000 kilometres (1,200 mi) across, and its area is around 2.8 million square kilometres (1.1×10^⁶ sq mi).

Various ice shelves, including the Filchner-Ronne Ice Shelf, fringe the Weddell sea. Some of the ice shelves on the east side of the Antarctic Peninsula, which formerly covered roughly 10,000 square kilometres (3,900 sq mi) of the Weddell Sea, had completely disappeared by 2002. The Weddell Sea has been deemed by scientists to have the clearest water of any sea. Researchers from the Alfred Wegener Institute, on finding a Secchi disc visible at a depth of 80 metres (260 ft) on 13 October 1986, ascertained that the clarity corresponded to that of distilled water.

In his 1950 book The White Continent, historian Thomas R. Henry writes: "The Weddell Sea is, according to the testimony of all who have sailed through its berg-filled waters, the most treacherous and dismal region on earth. The Ross Sea is relatively peaceful, predictable, and safe." He continues for an entire chapter, relating myths of the green-haired merman sighted in the sea's icy waters, the inability of crews to navigate a path to the coast until 1949, and treacherous "flash freezes" that left ships, such as Ernest Shackleton's Endurance, at the mercy of the ice floes.