Mario Oyarzabal

The Legal Adviser to the Argentine Foreign Ministry

Member of the United Nations International Law Commission

Membre associé de l’Institut de Droit international

General Editor and co-founder of the Latin American and Caribbean Journal of International Law

Former Argentine Ambassador to the Netherlands and representative to the international organisations and tribunals in The Hague

Ambassador Mario Oyarzábal is the Director General of International Legal Affairs and Legal Adviser of the Argentine Ministry of Foreign Affairs, International Trade and Worship since 2025, a position he also held between 2016 and 2020.

A career diplomat with the Argentine foreign service since 1997, Mario Oyarzábal served as Ambassador to the Kingdom of the Netherlands and Permanent Representative to the Organisation for the Prohibition of Chemical Weapons (OPCW) between 2020 and 2025, also representing Argentina before the International Court of Justice (ICJ), the Permanent Court of Arbitration (PCA), the International Criminal Court (ICC), the Hague Conference on Private International Law (HCCH) and the Common Fund for Commodities (CFC).

Previously, he was Deputy Permanent Representative of Argentina before the United Nations Security Council from 2013 to 2014 and Deputy Consul of Argentina in New York from 1998 to 2007.

In 2015, Ambassador Oyarzábal was the Lead negotiator for Argentina on the United Nations General Assembly Resolution 69/319 on the Basic Principles on Sovereign Debt Restructuring Processes.

From 2016 to 2020, he was the Argentine Commissioner to the International Whaling Commission (IWC).

He has acted as Head of Delegation and Delegate of Argentina to meetings of the Sixth Committee of the United Nations General Assembly, the International Seabed Authority (ISA), the International Maritime Organization (IMO), the Hague Conference on Private International Law (HCCH), the International Institute for the Unification of Private Law (UNIDROIT), the United Nations Commission on International Trade Law (UNCITRAL) and the Seventh Inter-American Conference on Private International Law (CIDIP VII) among others.

In 2025, he was decorated Knight Grand Cross of the Order of Orange-Nassau by King Willem-Alexander of the Netherlands.

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. In 2025 he was elected Chair of the ILC’ Drafting Committee.

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 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 Panel of Arbitrators and Conciliators of the International Centre for Settlement of Investment Disputes (ICSID), a position held between 2016 and 2024, 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.

He appeared before the International Court of Justice (ICJ) as Agent of Argentina in the Advisory Opinion on “The Legal Consequences of the Separation of the Chagos Archipelago from Mauritius in 1965” in 2019, and as Legal Counsel in the “Case concerning Pulp Mills on the River Uruguay (Argentina vs. Uruguay)” in 2010. He was also Legal Counsel in the Advisory Opinions of the International Tribunal for the Law of the Sea (ITLOS) on the “Responsibilities and Obligations of States Sponsoring Persons and Entities with respect to Activities in the International Seabed Area” in 2011, and on “Climate Change and International Law” in 2024. In 2025 he was Legal Counsel before the Council of the International Aviation Civil Organization (ICAO) on the Preliminary Objections in the Matter “The Bolivarian Republic of Venezuela and the Argentine Republic (2024)”.

He has taught private international law at the University of La Plata Law School as Adjunct Professor between 1995 and 2020, and public international law at the University of Buenos Aires Law School between 2008 and 2009, as well as at the Argentine Foreign Service Institute (ISEN) from 2009 to 2010 and from 2020 to 2021. In 2020 he delivered a Special Course at The Hague Academy of International Law on “The Influence of Public International Law upon Private International Law”. He has been invited by the Academy’s Curatorium to give the General Course in 2029.

He is General Editor and co-founder of the Latin American and Caribbean Journal of International Law.

PRINCIPAL DIPLOMATIC ASSIGNMENTS

The Legal Adviser to the Argentine Ministry of Foreign Affairs, 2016-2020, since 2025
Ambassador of the Argentine Republic to the Kingdom of the Netherlands and Permanent Representative to the Organisation for the Prohibition of Chemical Weapons, 2020-2025
Deputy Permanent Representative of the Argentine Republic to the United Nations Security Council, 2013-2014
Deputy Consul of Argentina in New York, 1998-2004, 2005-2007

LEGAL POSITIONS

Member of the United Nations International Law Commission, 2023-2027; Chair of the Drafting Committee, 2025
Arbitrator and Conciliator nominated under Art. 2 of Annexes V and VII of the United Nations Convention on the Law of the Sea, since 2017
Member of the Panel of Arbitrators and Conciliators of the International Centre for Settlement of Investment Disputes, 2016-2024
Member of the Permanent Court of Arbitration, 2019-2022
Member of the International Humanitarian Fact-Finding Commission established by Additional Protocol I to the 1949 Geneva Conventions, 2017-2021
Member of the Committee on the Election of the Prosecutor of the International Criminal Court, 2019-2020
Member of the Legal and Technical Commission of the International Seabed Authority, 2012-2013

INTERNATIONAL LITIGATION

Legal Counsel before the Council of the International Civil Aviation Organization on the Preliminary Objections in the Matter “The Bolivarian Republic of Venezuela and the Argentine Republic (2024)”, 2025
Legal Counsel for Argentina before the International Tribunal for the Law of the Sea in the Advisory Opinion on the “Climate Change and International Law”, 2024
Agent for the Argentine Republic before the International Court of Justice in the Advisory Opinion on “The Legal Consequences of the Separation of the Chagos Archipelago from Mauritius in 1965”, 2019
Legal Counsel for Argentina before the International Tribunal for the Law of the Sea in the Advisory Opinion on the “Responsibilities and obligations of States sponsoring Persons and Entities with respect to Activities in the International Seabed Area”, 2011
Legal Counsel for Argentina before the International Court of Justice in the “Case concerning Pulp Mills on the River Uruguay (Argentina v. Uruguay)’’, 2010

TEACHING

The Hague Academy of International Law, Special Course, 2020; General Course, 2029
Adjunct Professor at the University of La Plata Law School, 1995-2020
Professor at the Argentine Diplomatic Academy, 2009-2010, 2020-2021.
Adjunct Professor at the University of Buenos Aires Law School, 2008-2009

PROFESSIONAL AFFILIATIONS

EDUCATION

LLM (Master of Laws), Harvard Law School, 2005
Argentine Foreign Service Institute, 1995-1996
LLB (1990), Juris Doctor (1991), Notary (1992), University of La Plata Law School

LANGUAGES

Spanish (native), English and French (fluent), Italian and Portuguese (read).

Mario Oyarzabal

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