in 1989 Mackay was elected to the
Faculty of Advocates in 1955. He was appointed a
Queen's Counsel in 1965. He was
Sheriff Principal for Renfrew and Argyll from 1972 to 1974. In 1973 he became Vice-Dean of the Faculty on Advocates and from 1976 until 1979 served as its Dean, the leader of the Scots bar. In 1979, Mackay was appointed Lord Advocate, the senior law officer in Scotland, and was created a
life peer as
Baron Mackay of Clashfern, of
Eddrachillis in the District of Sutherland, taking his
territorial designation from his father's birthplace, a cottage beside Loch na Claise Fearna. After his retirement, Mackay sat in the House of Lords. He was also Commissary to the University of Cambridge until 2016. He is the editor-in-chief of ''
Halsbury's Laws of England'', the major legal work which states the law of England, first published in 1907; the post is usually held by a former Lord Chancellor. ==Family and religion==