Member of the UN International Law Commission (2008-2022); First Vice-Chair (2022); Special Rapporteur on Identification of customary international law (2012-2018)

Chair, Committee on the Use of Force, International Law Association (2011-2018)

Conciliator on UNCLOS Annex V list (conciliation) (2010- )

Arbitrator on UNCLOS Annex VII list (arbitration) (2010- )

Expert on UNCLOS Annex VIII list (special arbitration – marine scientific research) (2008- )

Member, Finance Committee, International Seabed Authority (1996-2006)

Chair of the Committee of Legal Advisers on Public International Law of the Council of Europe (CAHDI) (2007-2008); Vice-Chairman (2005-2006)

Chair of the Twenty-ninth Antarctic Treaty Consultative Meeting (ATCM XXIX), Edinburgh, June 2006

Member, Appeals Board, International Oil Pollution Compensation Fund 1992 (2004- )

Chair, Joint Appeals Board, International Seabed Authority (2008-2020)

Member, Appeals Board, European Centre for Medium-range Weather Forecasts (ECMWF) (2016- )

List of persons to be appointed to Arbitration Panels under UK-EU Withdrawal Agreement (2021- )

Member, Editorial Committee, British Yearbook of International Law

Member of the Advisory Board of the Max Planck Encyclopedia of Public International Law (Heidelberg)

Member, Fachbeirat, Max-Planck-Institut für auslãndisches öffentliches Recht und Völkerrecht, Heidelberg (2010-2018)

Member and Vice-Chair (2014), Chair (2019- ), Scientific and Development Policy Advisory Committee, Max Planck Foundation for International Peace and the Rule of Law, Heidelberg

Member, Advisory Board, Oxford International Organisations (OXIO)

Member, Advisory Board, The Law and Practice of International Courts and Tribunals

Member, Advisory Board, Indian Journal of International Law

Member, Board of Directors, International Law Students Association (ILSA) (2018- )