1764?–1820, Canadian fur trader and explorer, b. Scotland. His family took him to the colony of New York in 1774, and later he was sent to Canada. He entered (c.1779) a Montreal fur-trading firm and in a short time became partner of one of the firms that merged (1787) to form the North West Company. Given (1788) supervision of the important Athabasca fur district, Mackenzie set out (1789) from his headquarters at Fort Chipewyan on Lake Athabasca on the first of his two noted trips of exploration. After reaching Great Slave Lake, he followed the then unknown Mackenzie River to the Arctic Ocean.
Disappointed because the great river that now bears his name did not prove an avenue to the Pacific and unable to relinquish his hope of discovering a route to the Pacific, Mackenzie made careful preparations for a second expedition and set out again in 1793. He and his party fought their way up the Peace River and its tributary the Parsnip River, crossed the Continental Divide, and discovered the Fraser River, down which they traveled a short distance before they struck overland for the coast. Following the course of the Blackwater River, a western tributary of the Fraser, they reached and crossed the Coast Ranges to the Bella Coola River, which they descended, in a borrowed dugout, to its mouth in a tidal inlet of the Pacific. Thus Mackenzie completed the first overland journey across North America N of Mexico.
Shortly after this historic exploit, he left the West, never to return. His Voyages … to the Frozen and Pacific Oceans (1801) won him wide recognition and a knighthood in 1802. Mackenzie was elected in 1805 to the Legislative Assembly of Lower Canada, but he soon returned (1808) to Scotland, where he lived the rest of his life.