The son of
Charles Erskine, Earl of Mar, by his spouse Lady Mary, eldest daughter of George Maule, 2nd
Earl of Panmure, he was also brother of
John Erskine, 6th Earl of Mar. Educated as an
advocate, he was raised to the bench on 18 October 1706. He was nominated a Lord of Justiciary in place of David Home, Lord Crocerig on 6 June the same year, and took the title Lord Grange. On 27 July 1710 he succeeded
Adam Cockburn of Ormiston as
Lord Justice Clerk. He took no part in the
Jacobite rising of 1715, although there is little doubt that at times he was in communication with the
Jacobites; but was rather known for his piety and for his sympathy with the
Presbyterians. In 1724 he, and
David Erskine, Lord Dun purchased the forfeited
Earldom of Mar from the government, which they promptly reorganised, and sold off. His wife,
Rachel Chiesley, suspected her husband of infidelity, and after some years of unhappiness Grange arranged a plan for her abduction. In January 1732 she was taken in secret from Edinburgh to the
Monach Islands for two years, thence
Hirta in
St Kilda, where she remained for about ten years. From there, she was taken to
Assynt in
Sutherland, and finally to
Skye. To complete the idea that she was dead her funeral was publicly celebrated, but she survived until May 1745. Erskine himself was a "singular compound of good and bad qualities". In addition to his legal career he was elected to Parliament in 1734 and he survived the vicissitudes of the Jacobite rebellions unscathed. He was a
philanderer and over-partial to
claret, whilst at the same time deeply religious. This last quality would have been instrumental in any decision not to have his wife assassinated, and he did not marry his long-term mistress Fanny Lindsay until after he had heard of the first Lady Grange's death. Meanwhile, in 1734 Grange resigned his offices in the
Court of Session and Justiciary, and became a
Member of Parliament where he was a bitter opponent of
Sir Robert Walpole. His objective of being appointed
Secretary of State for Scotland was a failure. For a short time after leaving parliament he returned to the
Bar. Erskine stood in opposition to the
Witchcraft Act 1735, which – unlike previous laws – did not assume that witches actually existed and made pacts with Satan, but rather assumed that anyone who claimed to be actually practising
witchcraft was a cheater seeking to defraud people. The only figure to offer significant opposition to the Act was Erskine. Erskine not only fervently believed in the existence of witchcraft, but, it has been argued, also held beliefs that were deeply rooted in "Scottish political and religious considerations" and which caused him to reject the Act. His objection to the Act "marked him out as an eccentric verging on the insane" among Members of Parliament, and in turn his political opponents would use it against him; one of his staunchest critics,
Robert Walpole, who was then the
de facto Prime Minister of the country, allegedly stating that he no longer considered Erskine to be a serious political threat as a result of his embarrassing opposition to the Act. His Edinburgh mansion was on the east side of Niddry Wynd (later replaced by Niddry Street) off the
Royal Mile. He died in London on 20 January 1754, aged 75 years. ==Family==