He was admitted to the Faculty of Advocates in 1967 and appointed Queen's Counsel in 1981. He was called to the English Bar (Lincoln's Inn) in 1991. Lord Gill was an Advocate Depute from 1977 to 1979, and standing Junior Counsel to the Foreign and Commonwealth Office (1974–77), the Home Office (1979–81) and the Scottish Education Department (1979–81). He has been a member of the Scottish Legal Aid Board and the Scottish Valuation Advisory Council and Deputy Chairman of the Copyright Tribunal. Gill was appointed a Senator of the College of Justice in 1994, and was Chairman of the Scottish Law Commission from 1996 until 2001. Lord Gill was appointed Lord Justice Clerk and President of the Second Division of the Inner House of the Court of Session in November 2001.