This member of the weasel family has such long, lustrous fur that in the fur trade the American marten has been called the Canadian or American sable. Their fur varies in colour between individuals and by season. In summer it tends to be a tawny to dark brown, and in winter it is darker. Most individuals sport a paler (yellowish-orange) throat and bib.

Males are about 15% larger than females. The largest males can be 75 cm (2.5 ft.) long, including the tail. In different parts of the continent there is considerable variation in their size.

They are primarily nocturnal. Males are solitary and pugnacious, associating with females only in July and August during the mating season. The young are born and raised in grass-lined nests in hollow trees or in cavities in rocks.

Considered tree dwellers, American martens have semi-retractable claws to help them climb. They also spend considerable time on the ground, and are excellent swimmers.

Their principle source of food is mice, but squirrels, snowshoe hares and pikas are also popular. Martens also eat a variety of fruits and berries in summer, insects, birds, bird eggs and some carrion.

The American marten was once found in a broad belt across forested northern North America. Excessive trapping and destruction of their boreal forest habitat has depleted their numbers. Today, American martens remain only in scattered pockets, although much effort is being made to reintroduce martens to areas they formerly inhabited. Their insatiable curiosity and appetite, often mistaken for tameness, has made them rather easy victims for all sorts of traps.