[2][3] He was the third of the four children born to Kenneth 'Corc' Mackenzie (1731–1780) and his wife Isabella MacIver, from another prominent mercantile family in Stornoway.

He later became a merchant and held the tack of Melbost; his grandfather being a younger brother of Murdoch Mackenzie, 6th Laird of Fairburn.

[7] In 1776, during the American War of Independence, his father and uncle resumed their military duties and joined the King's Royal Regiment of New York as lieutenants.

[5] By 1779 (a year before his father's death at Carleton Island[4]), Mackenzie had a secured apprenticeship with Finlay, Gregory & Co., one of the most influential fur trading companies in Montreal, which was later administered by Archibald Norman McLeod.

[8] On behalf of the North West Company, Mackenzie journeyed to Lake Athabasca where, in 1788, he was one of the founders of Fort Chipewyan.

In the aftermath of the Nootka Crisis with Spain, he returned to Canada in 1792, and set out to find a route to the Pacific.

Accompanied by two native guides (one named Cancre), his cousin, Alexander MacKay, six Canadian voyageurs (Joseph Landry, Charles Ducette, François Beaulieu, Baptiste Bisson, Francois Courtois, Jacques Beauchamp), and a dog simply referred to as "our dog", Mackenzie left Fort Chipewyan on 10 October 1792, and travelled via the Pine River to the Peace River.

[15] From there he travelled to a fork on the Peace River arriving 1 November where he and his cohorts built a fortification that they resided in over the winter.

[citation needed] He had wanted to continue westward out of a desire to reach the open ocean, but was stopped by the hostility of the Heiltsuk people.

[20] Hemmed in by Heiltsuk war canoes, he wrote a message on a rock near the water's edge of Dean Channel, using a reddish paint made of vermilion and bear grease, and turned back east.

[24] In 1799 he left the Company and travelled to London to lobby on behalf of the Canadian fur trade.

(Later Simon Fraser and David Thompson worked to extend the Canadian fur trade and prevent U.S. incursion in what would be Canada.

[33] The Alexander Mackenzie rose (Explorer Series), developed in 1985 by Agriculture and Agri-Food Canada, was named in his honour.

[34] Between 1989 and 1993, the Mackenzie Bicentennial Sea-to-Sea Expeditions of Lakehead University attempted a segmented re-enactment of the journey between Montreal and Bella Coola, British Columbia, but was unable to complete the final overland 350 kilometres (220 mi) Grease Trail when its First Nation owners refused permission.