Judge Tompkins graduated from Gonville and Caius College, Cambridge, with a LLM(Hons) in 1984. After a period as a barrister at the independent Bar, he was appointed a District Court Judge in his home country of New Zealand in 1997.

Alongside his job as a judge, he teaches, writes and lectures on art crime generally, and art crime in war in particular. He teaches an 'Art in War' course, a component part of the annual Graduate Certificate in Art Crime and Heritage Protection offered by the Association for Research into Crimes against Art (ARCA) in Umbria, Italy each year.

Judge Tompkins is the author and editor of numerous books about art theft, art in war and authentification of art, the most recent of which is 2018's Plundering Beauty: A History of Art Crime during War (Lund Humphries, London).