Mr. Justice Donal O'Donnell was born in Belfast and educated at St Mary's C.B.S., University College Dublin (B.C.L.), King's Inns (B.L.) and the University of Virginia (LL.M).

He was called to the Irish Bar in 1982, commenced practice in 1983 and was called to the Bar of Northern Ireland in 1989. He took silk in 1995 and has practised in all Courts in Ireland, in the European Court of Justice (ECJ) and the European Court of Human Rights (ECtHR).

His father, Lord Justice Turlough O'Donnell, was a member of the Northern Ireland High Court and the Court of Appeal between 1971 and 1990 and subsequently became a part-time member of the Irish Law Reform Commission. Donal 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 and was appointed to the Supreme Court in 2010.