He was educated in the Edinburgh Academy, at the Magdalen College, Oxford, where he graduated with a Master of Arts and the University of Edinburgh, where he graduated with a Bachelor of Law. In the Second World War, he commanded the Scots Guards and was mentioned in despatches, reaching the rank of Captain. In 1951, he was called to the Bar and was made a Queen's Counsel in 1962, and a Bencher in 1976. He was Lord of Session under the judiciary title Lord Keith from 1971 to 1997.
On 10 January 1977, he was appointed Lord of Appeal in Ordinary and was made additionally a life peer with the title Baron Keith of Kinkel, of Strathummel in the District of Perth and Kinross. One year before he had been invested to the Privy Council. In 1996, he retired as Lord of Appeal and in 1997, he was awarded the Knight Grand Cross of the Order of the British Empire. It was humorously said within legal circles that wherever there was a negligence case, Lord Keith would always say 'no' (as in 'no damages').