Gregory was educated at Mardy House Secondary School, Aberdare Boys Grammar School and Birmingham University, where he obtained an honours degree in Law.

Gregory was called to the Bar by the Honourable Society of the Inner Temple in 1976. Having completed pupillages in London and Cardiff he accepted a tenancy in what was to become 30, Park Place Cardiff, where he built up a very substantial criminal and common law practice.

Gregory was appointed an Assistant Recorder in 1995 and a Recorder in 2000. He was Appointed Queen’s Counsel in 2003. He was in practice at 2 Paper Building from 2003-2010. Gregory became a member of Apex Chambers Cardiff in 2009 to date and became a member of Lombard Chambers in January 2011. From 2007 until 2010 Gregory was a Treasurer of the Wales and Chester Circuit and from 2010 to date, he was Leader of the Wales and Chester Circuit.

Gregory has established a very substantial practice in criminal law, fraud and regulatory work both in the United Kingdom and overseas.