Deeny was educated at Clongowes Wood School, Trinity College, Dublin and Queen's University, Belfast. During his time in Trinity College he acted as Auditor of the College Historical Society, the oldest undergraduate debating society in the world. He was called to the Bar of Northern Ireland in 1974 and took silk in March 1989. He was also called to the Bar in the Republic of Ireland (SC 1996), and in England (as a bencher in the Middle Temple). Deeny was appointed a High Court Judge on 6 September 2004, and was knighted some months afterwards.
He was appointed in 2000 to the UK Government's Spoliation Advisory Panel, which advises on claims relating to cultural objects lost during the Nazi era. He served two further terms before becoming chairman of the Panel in April 2010.
- "Birthday's today". The Telegraph. 25 April 2012. Retrieved 22 April 2014. "Mr Justice Deeny, 62"
- Biography in SLS course prospectus
- Debretts.com biography
- Archived notice of knighthood conferral
- Government press release
- LootedArt.com description of Spoliation Advisory Panel
- Northern Ireland Information Service archived statement on Arts Council appointments
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