Siofra O'Leary held various positions at the Court of Justice of the European Union until in April 2015 she was elected to replace Ann Power as Ireland's judge at the European Court of Human Rights. On 19 September 2022, she was elected President of the Court and became the first woman to hold that position when she took up office.

Before working at the Court, Dr. O’Leary was the Assistant Director for the Centre of European Legal Studies at the University of Cambridge and a Fellow of Emmanuel College. She was previously a Visiting Fellow at the Faculty of Law, University College Dublin, a Postdoctoral Fellow at the University of Cádiz, Spain and a Research Associate at the Institute for Public Policy Research in London.

She is the author of two books entitled The Evolving Concept of Community Citizenship (Kluwer, 1996) and Employment Law at the European Court of Justice (Hart Publishing, 2001) and has published extensively in academic journals and EU law monographs on the protection of fundamental rights in the EU, EU employment law, the free movement of persons and services and EU citizenship generally.