In 1992 he was appointed by the Department of Trade and Industry as an Inspector into the affairs of Mirror Group Newspapers plc (when it was owned by Robert Maxwell) and its IPO.

On 14 July 2003, Thomas became a Lord Justice of Appeal[5] and given the customary appointment to the Privy Council later that year.

[1] In October 2008, Thomas was appointed vice-president of the Queen's Bench Division and Deputy Head of Criminal Justice.

[8] On 26 September 2013, it was announced Thomas would become a life peer upon taking office as Lord Chief Justice.

[10] Following his introduction, as a serving member of the judiciary he was immediately disqualified from sitting in the House of Lords under section 137(3) of the Constitutional Reform Act 2005.

He is a member of the EU Financial Affairs Sub-Committee and chaired the Middle Level Bill Committee in 2018.

[14] He was appointed chairman of the Financial Markets Law Committee[clarification needed] in November 2017.

He returned to Essex Court Chambers in November 2017 and joined the Arbitrators at 24 Lincoln's Inn Fields.