[3] From 1988 to 1992, he served as a temporary sheriff,[4] and from 1989 to 1995 sat on the Board of the Criminal Injuries Compensation Authority.

He was duly created a life peer on 13 December 1995, as Baron Mackay of Drumadoon, of Blackwaterfoot in the District of Cunninghame,[5] and became a Privy Counsellor in 1996.

Between May 1997 and March 2000, he combined practice as a senior counsel with an active role in the House of Lords as Opposition Spokesman on Scotland and Constitutional Affairs.

[4] Mackay was also one of five members of the House of Lords, in addition to the twelve Lords of Appeal in Ordinary, eligible to form the quorum of the House required to hear and determine judicial business under ss.5&25 of the Appellate Jurisdiction Act 1876.

In October 2009 the judicial functions of the House of Lords were transferred to the new Supreme Court of the United Kingdom under Part 3 of the Constitutional Reform Act 2005, with the twelve Lords of Appeal in Ordinary becoming the inaugural Justices of the Court.