Aidan O’Neill is qualified to appear as counsel in Scotland, as well as in the courts of England and Wales. He is "roundly regarded as one of Scotland's finest human rights advocates" (The Firm, 2007). The Chambers Guide (2007) gave him their highest rating (Band 1) in civil liberties, describing him as "at the very top when it comes to human rights related matters" and the Chambers Guide (2009 and 2010) ranks him as Band 1 in employment law in Scotland stating that "he impresses solicitors with his work at the interface between human rights and employment law. Unsurprisingly, he has a particularly good grasp of European law and how that affects employment rights in the UK". The preface to the second edition of Clayton Tomlinson The Law of Human Rights (2009) observes that "the industry and scholarship of Aidan O’Neill QC astonish all who deal with him". And The Legal 500 (2009 edition) states that "he has ’outstanding turnaround times, probably unmatched at the Scottish Bar’, leads the field in human rights law and ‘is probably the leading counsel when it comes to questions of EU and competition law’. "
In addition to law degrees from Edinburgh and Sydney universities, Aidan O’Neill holds a degree in European and International and Comparative law from the European University Institute, Florence. In the academic year 2007-2008 he was the inaugural University Center for Human Values/Law and Public Affairs Fellow in Law and Normative Inquiry at Princeton University. In 2009, he was appointed to be Chairman of the Edinburgh Centre for Constitutional Law and, in the same year, was made an Honorary Fellow in the School of Law, University of Edinburgh.
He has written three legal text books to date: EC for UK Lawyers, a guide to the impact which EU law has on a wide variety of domestic fields of practice including company law, immigration and asylum, intellectual property, employment protection and discrimination, consumer law and private international law; Decisions of the European Court of Justice and their constitutional implications, a survey of the manner in which the ECJ created the conditions for a European constitution and has transformed the UK constitution; and Judicial Review in Scotland: a practitioner’s guide. He has also contributed chapters to a number of legal books, and is the author of many talks and articles in academic journals, particularly in the field of human rights, constitutional law and EU law. He has a particular interest in the inter-relationship between EU law, human rights law and public international law and in 2008 taught a semester-long seminar course at Princeton University on these issues. He also teaches a human rights elective seminar course in the Diploma in Legal Practice at Edinburgh Law School.
Aidan O’Neill has appeared as senior counsel before the European Court of Justice, the Judicial Committee of the Privy Council, the House of Lords, the Court of Session (Inner and Outer House), and the High Court of England & Wales (Administrative Division), as well as before the sheriff courts in Scotland and the county court in England and Wales. From 1997 to 1999, he was standing Junior Counsel to the Scottish Office (Education & Industry Department). Since taking silk in Scotland in 1999 he has maintained his high profile in discrimination and employment law issues, while his practice has also continued to develop strongly in the area of public law and judicial review (particularly in the area of fundamental rights) as well as more generally in constitutional law, post-devolution.