Professor of International Law at UCL. He has served on the Executive bodies of the American and European Societies of International Law and the International Law Association, and held visiting posts at various Arab and American universities, and was the Peace Fellow at the Åland Islands Peace Institute. His OUP book on international territorial administration and international trusteeship over people was awarded the book prize of the American Society of International Law; his publications on international law and the Palestinian people include articles in the Palestine Yearbook of International Law and the Journal of the History of International Law. He served as a legal advisor on international law to the PLO during the peace negotiations with Israel, and to several Palestinian human rights NGOs; as Counsel before the International Criminal Court concerning Palestine; and as Counsel before the International Court of Justice in the 2024 Advisory Opinion case on the illegality of Israel’s presence in the occupied Palestinian territory (OPT), in the 2025 Advisory Opinion case on Israel’s duties to the UN and States in the OPT, and in the current South Africa v Israel case concerning the Genocide Convention.