Ambassador Mario Oyarzábal specialises in Public and Private International Law.
In 2021, he was elected Member of the United Nations International Law Commission for the period of 2023 to 2027.
He was elected Associate member of the Institute of International Law (Institut de Droit international) at the 81st Session of Angers in 2023.
He is also currently a Member of the Panel of Arbitrators and Conciliators of the International Centre for Settlement of Investment Disputes (ICSID), a position held since 2016, as well as Arbitrator and Conciliator nominated under Art. 2 of Annexes V and VII of the United Nations Convention on the Law of the Sea (UNCLOS) since 2017. Previously, he served as Member of the Permanent Court of Arbitration (PCA) between 2019 and 2022, Member of the International Humanitarian Fact-Finding Commission (IHFFC) established by Additional Protocol I to the 1949 Geneva Conventions between 2016 and 2021, Member of the Committee on the Election of the Prosecutor of the International Criminal Court (ICC) between 2019 and 2020, and Member of the Legal and Technical Commission of the International Seabed Authority (ISA) between 2012 and 2013.