Henry Mackenzie was born in 1781 in Achnaclerach, Contin, Ross and Cromarty, Scotland.

He was a seigneurial agent, fur trader, merchant, Justice of the Peace, and militia officer. Henry McKenzie, a lesser-known figure, was the brother of Roderick, Donald, and James, and a cousin of Sir Alexander Mackenzie. He moved to Lower Canada shortly before 1800 and was hired as a clerk at Grand Portage, Minnesota. In 1803, he settled close to Montreal in the seigneury of Terrebonne, which belonged to Simon McTavish. He helped him manage it and as a seigneurial agent, he established contacts with grain dealers and exporters. In 1806, he obtained a commission as Justice of the Peace for the district of Montreal. At the beginning of the War of 1812, he joined the Terrebonne battalion of the militia as a major and later was promoted to lieutenant-colonel. In 1814, he purchased 2 of the 19 shares of McTavish, McGillivrays and Co. and became one of the partners of the Michilimackinac Company. In 1815, McGillivray put him in charge of public relations for the North West Company. The same year he joined the Beaver Club. He was a member of the Scotch Presbyterian congregation in Montreal, serving as its vice-chairman in 1819 and 1822, and chairman in 1823 and 1825.

In 1815, he married Ann Bethune, daughter of John Bethune and sister of Angus Bethune. He died on June 28, 1832, in Montreal, Quebec.