Scottish lawyer who gained the nickname “Bloody Mackenzie” for his prosecution of the Scottish Presbyterian Covenanters; he was founder of the Advocates' Library in Edinburgh, now the National Library of Scotland.

As king's advocate after August 1677, Mackenzie conducted, in the name of Charles II, a vigorous prosecution of Covenanters for their refusal to conform to the established church and, in consequence, has been compared to England's notorious Judge Jeffreys (Jeffreys, George Jeffreys, 1st Baron). As dean of the faculty of advocates, Mackenzie promoted the foundation of the Advocates' Library. After he refused to concur with measures to abolish anti-Catholic laws, Mackenzie was removed from office (1686) but was later reinstated (1688). After the Glorious Revolution (1688–89), he ceased to play an active political role.

Mackenzie wrote on religious issues and moral philosophy, but the bulk of his writing dealt with law. In Jus Regium (1684) and other works, he advocated doctrines of royal prerogative and the support of hereditary monarchy; yet he criticized intolerance and inhumanity. Mackenzie's Vindication of the Government of Scotland During the Reign of Charles II (1691) is a valuable primary source for that period. Mackenzie was knighted sometime before 1668.