Antonios is Associate Professor of Public International Law at the Faculty of Law of the University of Oxford and Fellow in Law at St Anne's College. He has been visiting lecturer at the Universities of Paris (Paris X – Nanterre) and London (King's College). He was previously lecturer in international law at University College London and at the University of Glasgow.
Antonios studied law in Athens, New York, and Oxford, during which time he also worked as a Researcher for the Hellenic Ministry of Foreign Affairs in Athens and New York, and for the UN Office in Geneva.
Antonios is a general international lawyer and has published in a number of areas of international law. His monograph, "Disobeying the Security Council", is on the responsibility of international organisations, and was published in 2011 (and re-issued in paperback with a new introduction in 2013) by Oxford University Press. He has also published in the fields of international dispute settlement, treaty law, immunities, the law of the sea, international investment law, and others.
Antonios has advised states, international organisations, and private entities on matters of public international law. He has advised and assisted counsel and members of tribunals or provided expert opinions in a number of cases before international and domestic courts and tribunals, including the International Court of Justice, EU courts, the European Court of Human Rights, ad hoc and ICSID arbitral tribunals, and the High Court of England and Wales. He has also provided training on international law to domestic judges, as well as diplomats, military officers, and other government officials.