In private life Mackenzie was a cultivated and learned gentleman with literary tendencies. He published in 1660
Aretina, which has been called the first
Scottish novel. He is remembered as the author of various graceful
essays. A contemporary antiquarian,
Alexander Nisbet, calls him "learned" and "renowned". Mackenzie wrote legal, political, and antiquarian books, including: •
The Science of Heraldry, Treated as a Part of the Civil Law of Nations: Wherein Reasons are Given for its Principles, and Etymologies of its Harder Terms (1680); •
Institutions of the Law of Scotland (1684); • ''Jus Regium: Or the Just and Solid Foundations of Monarchy in General, and More Especially of the Monarchy of Scotland: Maintain'd Against Buchannan, Naphtali, Dolman, Milton, &c.'' (1684), a major royalist tract; •
A Vindication of the Government in Scotland (1691); •
Antiquity of the Royal Line of Scotland (1686); •
Memoirs of the Affairs of Scotland from the Restoration of Charles II (1821). Mackenzie took part in the
Midlothian trials for
witchcraft in 1661, and defended the alleged witch Maevia. He later wrote at length of his experience with witchcraft trials. He did not endorse the sceptical position, but stated that witches were fewer than common belief made out. He attributed confessions to the use of torture. His
Laws and Customs of Scotland in Matters Criminal (1678) was the first textbook of
Scottish criminal law. In it Mackenzie defended the use of
judicial torture in Scotland as legal. He said it was seldom used. In the aftermath of the
Rye House Plot Charles II authorised the use of torture against
William Spence, secretary to
Archibald, Earl of Agyll, who was moved to Scotland. The Scottish privy council was reluctant, but eventually went beyond Scottish law in torturing Spence. Mackenzie visited
William Carstares in prison in London, caught up in the same investigation, to warn him of the consequences of stubborn behaviour under questioning. •
Religio Stoici (1663); •
A Moral Essay preferring Solitude to Public Employment (1665); •
Moral Gallantry (1667); and •
The Moral History of Frugality (1691). ==Legacy==