Lord Mance attended Charterhouse School, then studied law at University College, Oxford. He was called to the Bar by Middle Temple in 1965, and joined 7 King's Bench Walk, where he practicsed insurance and reinsurance, international trade, shipping, and other areas of commercial law. He was appointed Queen's Counsel in 1982, and was made a Recorder in 1990. In 1993, he became a Judge of the Queen's Bench Division, and was nominated to sit as a Commercial Judge. He was appointed Lord Justice of Appeal in 1999, and Lord of Appeal in Ordinary in 2005. Upon the creation of the Supreme Court of the United Kingdom in 2009, he became one of the Court's first Justices. He served as Vice-President of the Supreme Court from 2017 to 2018. After retiring from the English Bench in 2018, he became a Judge of the Singapore International Commercial Court and resumed private practice as a commercial arbitrator.

Lord Mance's pastimes include tennis, music, and walking, and he enjoys learning foreign languages.