Lord Cullen was educated at the High School of Dundee, and was a graduate of St Andrews and Edinburgh Universities. He was in practice as an advocate until 1986 when he became a judge. In 2001 he was appointed to be the Lord President of the Court of Session and the Lord Justice General of Scotland. He retired in 2005.
During the time when he was a judge he conducted the public inquiries into the Piper Alpha disaster in 1988; the shootings at Dunblane Primary School in 1996, and the Ladbroke rail crash in London in 1999.
After he retired he was a part-time judge in Qatar, and carried out a review of the legislation for fatal accident inquiries in Scotland.
He is a member of the Privy Council. In 2003 he was made a life peer, and in 2007 a knight of the Order of the Thistle.
He was elected a Fellow of the Royal Society of Edinburgh in 1993, and an Honorary Fellow of the Royal Academy of Engineering in 1995. He was the Chancellor of Abertay University from 2009 to 2019.