Entirely located in Canada, the Southern Hudson Bay taiga covers an area of approximately 373,735 square kilometres (144,300 sq mi) and crosses the provinces of Manitoba, Ontario, and the western portion of Quebec.

[3] It covers nearly a quarter of Ontario's landmass, and 3.6% of Canada's total area,[4][5] Its historical prominence is due to the harshness endured by pioneer explorers who established fortifications for Hudson's Bay Company, and as a result of regional wars between France and Britain.

[1] Its soils, which are primarily Gelic and Dystric Histosols and Eutric Gleysols, are characterized by shallow layers of permafrost, slightly acidic pH levels, and hydromorphic conditions.

The Palaeozoic and Proterozoic sedimentary deposits overlaying the bedrock[3] have formed into a wide and level plain characterised by raised beaches and river deltas,[8] with an elevation rarely exceeding 120 m.[9] The relatively flat land slopes gently toward the two bays, which act as a drainage basin for the region.

[11] Typical seasonal conditions in the Southern Hudson Bay taiga consist of brief, cool summers with significant daylight, and cold winters with prolonged darkness.

[3] Vegetation is somewhat limited, with the northern areas abutting the Arctic Archipelago Marine being nearly treeless, whereas the southern extent, adjacent to the Boreal Shield, have open forest.

[11][13] Belonging to the circumboreal floristic region, the Southern Hudson Bay taiga contains a total of 1178 different plant species – none of which are considered endemic to the area.

[15] The major plant communities in this ecoregion, which are characteristic of the taiga biome, primarily consist of black spruce (Picea mariana) and tamarack (Larix laricina) forests.

[1] In terms of species composition, the animal populations of the Southern Hudson Bay taiga are largely transitional between those of the Central Canadian Shield forests and Low Arctic tundra.

[15] The coastal areas of southern Hudson Bay are home to polar bears (Ursus marinus), arctic foxes (Vulpes lagopus), seals (Phocidae), beluga whales (Delphinapterus leucas), and tundra swans (Cygnus columbianus).

Other species which can be found throughout the entirety of the ecoregion are caribou (Rangifer tarandus), snowshoe hare (Lepus americanus), and Canada goose (Branta canadensis).

It was part of a larger area referred to as Rupert's Land in which the Hudson's Bay Company had exclusive commercial rights until it was sold to the Canadian government in 1870.