Philippa’s practice covers all aspects of public international law. She acts for state and private entities in domestic and international courts on a wide range of issues. These include state and diplomatic immunities, territorial and maritime boundaries, treaty obligations, law of the sea, climate change, state responsibility, human rights, humanitarian law, law of international organisations and international criminal law.
She has been described as “the foremost expert on state immunity” and is counsel, often unled, in precedent-setting cases in international and English courts. In 2025 alone, she conducted advocacy before the UK Supreme Court in two cases on State immunity. Philippa advises on all aspects of immunity, including immunity from enforcement, diplomatic status, and related concepts such as act of state.In 2025, she was elected to the Institut de droit international, whose membership comprises the world’s 132 leading international lawyers.
Philippa is a specialist in relation to the International Court of Justice (ICJ). She served as the Legal Officer and Special Assistant to Judge Rosalyn Higgins GBE KC during her presidency and in this capacity was involved in 15 inter-state cases. Philippa has since appeared as counsel and advocate in a further 12 ICJ cases. She is currently instructed on cases representing half the ICJ’s docket. She also appears before the International Tribunal for the Law of the Sea and the European Court of Human Rights.
As a third strand to her practice, Philippa is counsel in inter-State arbitrations involving critical foreign relations issue, such as national defence, energy and water security.
She is full Professor of Public International Law at the University of Oxford and a Fellow of Exeter College. She is Co-founder and Director of the Oxford Institute of Technology and Justice.
Philippa was awarded “International Law Junior 2025” by Legal500. She was shortlisted for 2022 “Barrister of the Year” by The Lawyer. She is ranked as a top junior and ‘ Star Individual’ in Public International Law in the directories.
Privacy noticeExample cases
- UK Supreme Court: Shehabi v Bahrain UKSC/2024/0152: Conducted advocacy in the Supreme Court on behalf of respondents in precedent-setting case on territorial tort exception to State immunity (s 5 UK SIA) involving allegations of spyware use against human rights activists.
- UK Supreme Court: Infrastructure Services Luxembourg S.A.R.L v Spain UKSC/2024/0155: Conducted advocacy on behalf of the respondent on whether Article 54(1) of the ICSID Convention constitutes a submission to the jurisdiction by prior agreement for the purposes of s2(2) UK SIA. The case has global repercussions for investment arbitration under the ICSID Convention.
- UK Supreme Court: Basfar v Wong [2022] UKSC 20: Counsel to the claimant in the first case in the world in which a leading court has concluded that the alleged exploitation of a domestic worker in circumstances of modern slavery falls within the “commercial activity” exception to diplomatic immunity in Article 31(1)(c) of the Vienna Convention on Diplomatic Relations 1961.
- English Court of Appeal: Shehabi v Kingdom of Bahrain [2024] EWCA Civ 1158: Unled in Court of Appeal as counsel to claimants in precedent-setting case on territorial tort exception to State immunity (s 5 UK SIA) involving allegations of spyware use against human rights activists.
- English High Court: Al Masarir v Kingdom of Saudi Arabia [2022] EWHC 2199: Counsel to the claimant in a case ruling that Saudi Arabia is not immune under the UK State Immunity Act for alleged use of spyware to infiltrate the iPhones of a prominent human rights activist. The first case to find an exception to sovereign immunity for allegations related to spyware.
- Inter-State Arbitration: Indus Waters Treaty Arbitration (Pakistan v India): Counsel to Pakistan in a dispute over the interpretation and application of the Indus Waters Treaty 1960 to the design and operation of run-of-river hydro-electric projects on the Indus, Jhelum, and Chenab Rivers and their tributaries.
- Inter-State Expert Proceeding: Indus Waters Treaty Neutral Expert Proceedings (India v Pakistan): Counsel to Pakistan in proceedings before an expert engineer (Neutral Expert) concerning the Kishenganga and Ratle Hydroelectric Plants.
- International Court of Justice (ICJ): Legal Consequences arising from the Policies and Practices of Israel in the Occupied Palestinian Territory, including East Jerusalem: Counsel to Belize in advisory proceedings requested by the UN General Assembly.
- International Court of Justice, Obligations of States in respect of Climate Change: Counsel to Tuvalu in advisory proceedings requested by the UN General Assembly.
- ICJ: Guatemala’s Territorial, Insular and Maritime Claim (Guatemala/Belize): Counsel to Belize in dispute with Guatemala over land and insular territories and maritime areas pertained to those territories.
- ICJ: Application of the Convention on the Prevention and Punishment of the Crime of Genocide in the Gaza Strip (South Africa v. Israel): Counsel to The Maldives in advisory proceedings requested by the UN General Assembly.
- ICJ: Questions of jurisdictional immunities of the State and measures of constraint against State-owned property (Germany v. Italy): Counsel to Italy in dispute with Germany concerning alleged breaches of State immunity by Italian courts in cases concerning war crimes and crimes against humanity.
- ICJ: Allegations of Genocide under the Convention on the Prevention and Punishment of the Crime of Genocide (Ukraine v. Russian Federation): Counsel to the United Kingdom in a case in which it is intervening under the Genocide Convention.
- ICJ: Application of the Convention on the Prevention and Punishment of the Crime of Genocide (The Gambia v. Myanmar): Counsel to the Maldives in a case in which it is intervening under the Genocide Convention.
- ITLOS: Request for an Advisory Opinion submitted by the Commission of Small Island States on Climate Change and International Law: Counsel to 9 small island States in case on the prevention, reduction and mitigation of GHG emissions as marine pollution and the obligation to protect the marine environment in the context of climate change.
- European Court of Human Rights: Ukraine v. Russia (X): Counsel to Ukraine in a case against the Russian Federation arising from the invasion of Ukraine in February 2022.
- Inter-State Arbitration: The ‘Enrica Lexie’ Incident (Italy v India): Counsel to the Italian Republic in a case before the Permanent Court of Arbitration concerning an incident approximately 20.5 nautical miles off the coast of India involving the “Enrica Lexie”, an oil tanker flying the Italian flag, and India’s subsequent exercise of criminal jurisdiction over the vessel and two Italian marines from the Italian Navy.
- UK Supreme Court: Reyes v Al-Malki [2017] UKSC 61: counsel to the intervenor (Kalayaan) in a case on diplomatic immunity. The appeal was unanimously allowed, with the court holding that the former diplomat did not enjoy immunity for the employment and alleged mistreatment of his domestic servant (led by Richard Hermer KC).
- The Freedom And Justice Party and others, R (On the Application Of) v The Secretary of State for Foreign and Commonwealth Affairs and another (Rev 2) [2018] EWCA Civ 1719: counsel for the appellants in a case concerning special missions immunity and allegations of torture (led by Sudhanshu Swaroop KC).
Public international law
Philippa advises clients from all over the world on a wide range of international law issues. She appears as counsel in cases involving international law in the English courts as well as counsel before international courts, including the International Court of Justice, the European Court of Human Rights and the International Tribunal for the Law of the Sea. During her time at the ICJ, she worked on 15 cases involving the law of the sea, territorial sovereignty, immunities, genocide, the use of force, human rights, diplomatic protection, and environmental matters. Philippa has since appeared as counsel and advocate in a further 12 ICJ cases as well as in groundbreaking human rights and climate change cases.
Philippa is full Professor of Public International Law at University of Oxford and has published 6 books and more than 60 articles and chapters on international law.
Her expertise is recognized by her appointment to the International Advisory Panel for the American Law Institute’s project Restatement Fourth, Foreign Relations Law of the United States and to the Attorney General’s Public International Law B Panel of Counsel. She was Director of Studies for the Centenary Edition of the Hague Academy of International Law.
Her lecture for the United Nations Audiovisual Library of International Law is available here.
- UK Supreme Court: Shehabi v Bahrain UKSC/2024/0152: Conducted advocacy in the Supreme Court on behalf of respondents in precedent-setting case on territorial tort exception to State immunity (s 5 UK SIA) involving allegations of spyware use against human rights activists.
- UK Supreme Court: Infrastructure Services Luxembourg S.A.R.L v Spain UKSC/2024/0155: Conducted advocacy on behalf of the respondent on whether Article 54(1) of the ICSID Convention constitutes a submission to the jurisdiction by prior agreement for the purposes of s2(2) UK SIA. The case has global repercussions for investment arbitration under the ICSID Convention.
- ICJ Right to Strike Advisory Opinion: Counsel and Advocate for the United Kingdom on whether the right to strike is protected under Convention No. 87.
- International Court of Justice (ICJ): Legal Consequences arising from the Policies and Practices of Israel in the Occupied Palestinian Territory, including East Jerusalem: Counsel to Belize in advisory proceedings requested by the UN General Assembly.
- International Court of Justice, Obligations of States in respect of Climate Change: Counsel to Tuvalu in advisory proceedings requested by the UN General Assembly.
- ICJ: Guatemala’s Territorial, Insular and Maritime Claim (Guatemala/Belize): Counsel to Belize in dispute with Guatemala over land and insular territories and maritime areas pertained to those territories.
- ICJ: Application of the Convention on the Prevention and Punishment of the Crime of Genocide in the Gaza Strip (South Africa v. Israel): Counsel to The Maldives in advisory proceedings requested by the UN General Assembly.
- ICJ: Questions of jurisdictional immunities of the State and measures of constraint against State-owned property (Germany v. Italy): Counsel to Italy in dispute with Germany concerning alleged breaches of State immunity by Italian courts in cases concerning war crimes and crimes against humanity.
- ICJ: Allegations of Genocide under the Convention on the Prevention and Punishment of the Crime of Genocide (Ukraine v. Russian Federation): Counsel to the United Kingdom in a case in which it is intervening under the Genocide Convention.
- ICJ: Application of the Convention on the Prevention and Punishment of the Crime of Genocide (The Gambia v. Myanmar): Counsel to the Maldives in a case in which it is intervening under the Genocide Convention.
- ITLOS: Request for an Advisory Opinion submitted by the Commission of Small Island States on Climate Change and International Law: Counsel to 9 small island States in case on the prevention, reduction and mitigation of GHG emissions as marine pollution and the obligation to protect the marine environment in the context of climate change.
- European Court of Human Rights: Ukraine v. Russia (X): Counsel to Ukraine in a case against the Russian Federation arising from the invasion of Ukraine in February 2022.
- ICJ: Legal consequences of the separation of the Chagos Archipelago from Mauritius in 1965: Counsel to the United Kingdom in a request by the UN General Assembly.
- ICJ various cases: Counsel to various States in cases on maritime delimitation, territorial sovereignty, sanctions and immunities in international law.
- ITLOS: Request for an Advisory Opinion submitted by the Commission of Small Island States on Climate Change and International Law: Counsel to 9 small island States in case on the prevention, reduction and mitigation of GHG emissions as marine pollution and the obligation to protect the marine environment in the context of climate change.
- ITLOS Case No. 24 The “Enrica Lexie” Incident (Italy v India): Counsel to the Italian Republic. PCA Case No. 2015-28: The “Enrica Lexie” Incident (Italy v India): Counsel to the Italian Republic.
- Counsel to an international organization in an arbitration on its immunities in the UK.
Human rights
Philippa acts and advises in relation to a wide range of human rights issues before domestic and international courts and bodies. She is the co-author of The Right to a Fair Trial in International Law (OUP 2021, with Amal Clooney), which has been described ‘a must-read book for everyone in the field: judges, scholars, students, civil servants, NGOs and all over the world’ (Judge Tulkens, former Vice-President of the ECtHR), ‘the definitive work now on fair trial rights’ (Professor van Schaack, Stanford University), ‘An outstanding book … It creates the basis by which a vigilance can be exercised’ (Zeid Ra’ad Zeid Al Hussein, former UN High Commissioner for Human Rights), and ‘essential for judges at all stages of proceedings and academics and students’ (Judge Sir Howard Morrison KCMG CBE KC, former British Judge at the International Criminal Court. She has also written books on genocide and human dignity.
Her human rights cases include groundbreaking cases on accountability and immunity for alleged human rights violations (modern slavery, high tech surveillance and harassment) and characterising climate change as a human rights issue. She has represented survivors of human rights abuses and advised on legal options for reparations for Ukraine.
She is a Founding Board Member of the Clooney Foundation for Justice and has a substantial pro bono practice before English courts, international courts and human rights treaty bodies.
- UK Supreme Court: Basfar v Wong [2022] UKSC 20: Counsel to the claimant in the first case in the world in which a leading court has concluded that the alleged exploitation of a domestic worker in circumstances of modern slavery falls within the “commercial activity” exception to diplomatic immunity in Article 31(1)(c) of the Vienna Convention on Diplomatic Relations 1961.
- English Court of Appeal: Shehabi v Kingdom of Bahrain [2024] EWCA Civ 1158: Unled in Court of Appeal as counsel to claimants in precedent-setting case on territorial tort exception to State immunity (s 5 UK SIA) involving allegations of spyware use against human rights activists.
- English High Court: Al Masarir v Kingdom of Saudi Arabia [2022] EWHC 2199: Counsel to the claimant in a case ruling that Saudi Arabia is not immune under the UK State Immunity Act for alleged use of spyware to infiltrate the iPhones of a prominent human rights activist. The first case to find an exception to sovereign immunity for allegations related to spyware.
- International Court of Justice (ICJ): Legal Consequences arising from the Policies and Practices of Israel in the Occupied Palestinian Territory, including East Jerusalem: Counsel to Belize in advisory proceedings requested by the UN General Assembly.
- International Court of Justice, Obligations of States in respect of Climate Change: Counsel to Tuvalu in advisory proceedings requested by the UN General Assembly.
- ICJ: Application of the Convention on the Prevention and Punishment of the Crime of Genocide in the Gaza Strip (South Africa v. Israel): Counsel to Belize in advisory proceedings requested by the UN General Assembly.
- ICJ: Questions of jurisdictional immunities of the State and measures of constraint against State-owned property (Germany v. Italy): Counsel to Italy in dispute with Germany concerning alleged breaches of State immunity by Italian courts in cases concerning war crimes and crimes against humanity.
- ICJ: Allegations of Genocide under the Convention on the Prevention and Punishment of the Crime of Genocide (Ukraine v. Russian Federation): Counsel to the United Kingdom in a case in which it is intervening under the Genocide Convention.
- ICJ: Application of the Convention on the Prevention and Punishment of the Crime of Genocide (The Gambia v. Myanmar): Counsel to the Maldives in a case in which it is intervening under the Genocide Convention.
- ITLOS: Request for an Advisory Opinion submitted by the Commission of Small Island States on Climate Change and International Law: Counsel to 9 small island States in case on the prevention, reduction and mitigation of GHG emissions as marine pollution and the obligation to protect the marine environment in the context of climate change.
- European Court of Human Rights: Ukraine v. Russia (X): Counsel to Ukraine in a case against the Russian Federation arising from the invasion of Ukraine in February 2022.
- UK Supreme Court: Reyes v Al-Malki[2017] UKSC 61: Counsel to the intervenor, Kalayaan, in a case on immunity and modern slavery.
- English Court of Appeal: The Freedom and Justice Party and others, R (On the Application Of) v Secretary of State for Foreign and Commonwealth Affairs & Anor [2018] EWCA Civ 1719 and The Freedom and Justice Party and others, R (On the Application Of) v Secretary of State for Foreign and Commonwealth Affairs & Anor[2016] EWHC 2010 (Admin): Counsel to Freedom & Justice Party on allegations of torture and the customary international law on special missions immunity.
- Legal advisor to the UN Special Rapporteur on Counter-Terrorism and Human Rights regarding the inquiry into the legality of drones (2013).
Arbitration
Philippa specializes in inter-State arbitrations before tribunals of senior international jurists and technical experts for disputes that are often the defining issues in foreign relations between States. She is also counsel in arbitration-related proceedings before English courts involving resistance to or enforcement of awards and issues of State immunity.
In 2024, Philippa was invited to give the 3VB & NUS Arbitration Lecture on “Double Waiver Immunity ad Ripple Effects”. Philippa was invited to speak on immunity and act of state issues in arbitration on the occasion of the 125th Anniversary of the Commercial Court.
- Inter-State Arbitration: Indus Waters Treaty Arbitration (Pakistan v India): Counsel to Pakistan in a dispute over the interpretation and application of the Indus Waters Treaty 1960 to the design and operation of run-of-river hydro-electric projects on the Indus, Jhelum, and Chenab Rivers and their tributaries.
- Inter-State Expert Proceeding: Indus Waters Treaty Neutral Expert Proceedings (India v Pakistan): Counsel to Pakistan in proceedings before an expert engineer (Neutral Expert) concerning the Kishenganga and Ratle Hydroelectric Plants.
- Inter-State Arbitration: The ‘Enrica Lexie’ Incident (Italy v India): Counsel to the Italian Republic in a case before the Permanent Court of Arbitration concerning an incident approximately 20.5 nautical miles off the coast of India involving the “Enrica Lexie”, an oil tanker flying the Italian flag, and India’s subsequent exercise of criminal jurisdiction over the vessel and two Italian marines from the Italian Navy.
- Judicial Committee of the Privy Council: Botas Petroleum Pipeline Corporation v Tepe Insaat Sanayii AS [2018] UKPC 31: Counsel to Tepe in a case before the Judicial Committee of the Privy Council on immunities from enforcement against State property.
- Commercial Court: PAO Tatneft v Ukraine[2018] EWHC 1797 (Comm): counsel to Ukraine in a case concerning an effort to enforce a US$112 million investment BIT award in favour of Russian oil producer Tatneft against Ukraine, raising issues of immunity.