[6] In 1990, he became a recorder, and on 25 October 1993 was appointed a High Court judge,[7] serving in the Queen's Bench Division, and received the customary knighthood.

[6] On 3 October 2005, he was appointed a Lord of Appeal in Ordinary with a Life Peerage as Baron Mance, of Frognal in the London Borough of Camden.

[10] On 1 October 2009, he and nine other Lords of Appeal became Justices of the Supreme Court upon that body's inauguration.

In a speech to the Hoge Raad in The Netherlands in 2013, Lord Mance described the creation of the Supreme Court as the consequence of a "back of an envelope plan", which "took some years to straighten out".

[11] He has also served as chairman of the Banking Appeals Tribunal (1992–93), chairman of the Consultative Council of European Judges (2000), president of the British Insurance Law Association (2000–02) and trustee of the European Law Academy (2003).