Lord Thomas read law at Trinity Hall, Cambridge and the University of Chicago Law School. He practiced at the Commercial Bar in London from what is now Essex Court Chambers from 1972 to 1996, becoming a QC in 1984.
He was appointed to the High Court of England and Wales in 1996. He was a Presiding Judge in Wales (1998-2001), Judge in Charge of the Commercial Court (2002-3), the Senior Presiding Judge for England and Wales (2003 to 2006), Vice-President of the Queen’s Bench Division (2008-2011), President of the Queen’s Bench Division (2011-2013) and Lord Chief Justice of England and Wales (2013 – 2017). He has now returned to Essex Court Chambers
He is a founder member of the European Law Institute and is currently a member of its Executive Committee; he was President of the European Network of Councils for the Judiciary (2008-2010).
He is Chairman of the Commission on Justice in Wales established by the Welsh Government and Chairman of the Financial Markets Law Committee.
He is Chancellor of the Aberystwyth University, a Fellow of the Learned Society of Wales and an Honorary Fellow or Fellow of several Universities.