Aidan O'Neill

Aidan O'Neill (born 1961) is a Scottish advocate, barrister, and King's Counsel.

He has pleaded almost thirty times before the Supreme Court of the United Kingdom and House of Lords, as well before the Court of Justice of the European Union and the European Court of Human Rights.

He appeared for Joanna Cherry MP before the Supreme Court of the United Kingdom in the September 2019 case relating to the prorogation of Parliament.

Career O'Neill read Law from 1978 to 1982, obtaining a First Class LL.B. (Hons.) degree from the University of Edinburgh. He then studied a Diploma in Legal Practice also at Edinburgh from 1982 to 1983.

From 1997 to 1999 O'Neill was Standing Junior Counsel to the Scottish Office Education and Industry Department. He joined his present London chambers, Matrix Chambers of Gray's Inn, London in 2000, and became a member in 2010.

He was appointed by a cross-party group of 75 MPs and peers to contest a case for judicial review against the Government in the Scottish Court of Session. He went on to receive widespread media coverage in September 2019 upon representing the group including Joanna Cherry MP against the government (represented by Advocate General for Scotland, Lord Keen QC) in the case of R (Miller) v Prime Minister; Cherry & Ors v Advocate General for Scotland.

In the case he contested the use of prorogation powers by Prime Minister Boris Johnson.

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