Donal Gerard O'Donnell (born 25 October 1957^[1]) is an Irish judge who is the Chief Justice of Ireland since October 2021. He has served as a Judge of the Supreme Court of Ireland since January 2010. He practised as a barrister between 1982 and 2010, specialising in commercial law and public law.

He was born in Belfast, in 1957.^[2] He was educated at St. Mary's Christian Brothers' Grammar School, Belfast, University College Dublin, King's Inns and the University of Virginia.^[3] While attending University College Dublin, he won the 1978 Irish Times Debate with Conor Gearty for the UCD Law Society.^[4] He graduated from Virginia in 1983, where he wrote a research paper comparing equality under the US and Irish constitutions, supervised by A.E. Dick Howard.^[5] Janet Napolitano was also among the class of 1983.^[6]

His brother Turlough O'Donnell SC is former Chairman of the Bar Council of Ireland.^[7] He comes from a legal family, his father, The Rt. Hon Turlough O'Donnell PC, was a member of the High Court of Northern Ireland and of the Court of Appeal of Northern Ireland between 1971 and 1990.^[8]

He was called to the Bar of Ireland in 1982. He was then later called to the Bar of Northern Ireland in 1989.^[9] He became a Senior Counsel in October 1995.^[10] He has practised in all courts in Ireland, Northern Ireland, European Court of Justice (ECJ) and the European Court of Human Rights (ECHR).^[3] He was known for his speciality in constitutional law, frequently appearing on behalf of the State.^[11][2] In 1995-96 he represented the BTSB in the Brigid McCole case, eventually settling her case for damages. He successfully represented the applicants from the Garda Síochána after the death of John Carthy in a constitutional challenge which limited the powers of investigation of the Oireachtas,^[12] which led to the unsuccessful Thirtieth Amendment of the Constitution.^[13] He acted for the State in Zappone v. Revenue Commissioners, Roche v Roche and Miss D.^[9][2] In Michael Ring's challenge to a ban on a dual mandate he acted for the State and represented Micheál Martin in an action taken by Kathy Sinnott challenging the results of the 2002 general election in Cork South-Central.^[14][15] He was counsel for Michael Lowry at the Moriarty Tribunal.^[9] In 2002, he represented eighteen religious groups in a negotiation with the Minister for Education Michael Woods.^[16] He acted for Ireland in the European Court of Human Rights in 2009 in A, B and C v Ireland.^[17]

O'Donnell's practice also extended to commercial law. He and Paul Gallagher acted for a group of tobacco companies in 2004 challenging restrictions of tobacco advertising and he appeared for the estate of James Joyce in a copyright action against Cork University Press in 2000.^[18][19] He represented the Beef Industry Development Society Ltd in a 2008 case in the ECJ which clarified the meaning of an agreement under Article 101 of the Treaty on the Functioning of the European Union.^[20] In 2007 he and Paul Anthony McDermott acted for Elin Nordegren in libel proceedings against The Dubliner.^[21] He also appeared in cases involving insolvency law, employment law, company law and contract law.^{[22][23][24][25]}

O'Donnell was a member of the Law Reform Commission from 2005 to 2012. He became a Bencher of the King's Inns in 2009.^[3]

O'Donnell was appointed to the Supreme Court in 2010. He was appointed directly from practice to Ireland's highest court, a rare direct appointment.^[26] His appointment followed Nicholas Kearns becoming President of the High Court.^[27]

There have been several distinctive and innovative features of his Supreme Court judgments, including writing joint opinions and opting to delay a declaration of unconstitutionality, in lieu of no declaration at all, to enable the government to take action before a judgment takes effect.^[11] Ruadhán Mac Cormaic of The Irish Times says O'Donnell has a reputation for elegant writing and having a "socially liberal" approach.^[11]

He is married to Mary Rose Binchy, an artist,^[11] with whom he has four children.^[9]