Reed was Standing Junior Counsel to the Scottish Education Department from 1988 to 1989, and to the Scottish Office Home and Health Department from 1989 to 1995. He was appointed Queen's Counsel in 1995, and Advocate Depute in 1996. He was appointed a Senator of the College of Justice, a judge of the Court of Session and High Court of Justiciary, the country's College of Justice, in 1998, with the judicial title, Lord Reed. He sat initially as a Judge of the Outer House, becoming Principal Commercial Judge in 2006. He has been one of the United Kingdom's "ad hoc" judges at the European Court of Human Rights, and sat in the Grand Chamber judgements on the appeals of the killers of James Bulger in 1999. Between 2002 and 2004, he was an expert advisor to the EU/Council of Europe Joint Initiative with Turkey. He was promoted to the Inner House (First Division) in 2008, and appointed to the Privy Council. He sat on the UK Supreme Court during the illness of Lord Rodger of Earlsferry, along with Lord Clarke, and succeeded Lord Rodger.