Oonagh Sands > Fietta LLP > London, England > Lawyer Profile

Fietta LLP


Oonagh Sands is a dually qualified English and US lawyer. She is an English-qualified Solicitor and Solicitor-Advocate (Higher Courts Civil Proceedings) and an Attorney in New York State as well as the District of Columbia. The Legal 500 has recognised Oonagh as a “Rising Star” in public international law.

She has significant experience representing sovereign States and their State-owned entities, as well as individuals and private entities, before leading world dispute resolution fora.  She has represented clients before the International Court of Justice, the Permanent Court of Arbitration, as well as investor-State arbitral tribunals constituted under ICSID, ICSID Additional Facility, UNCITRAL, SCC and ICC Rules.  Oonagh has counselled States on a broad range of public international law issues, including territorial and maritime boundary disputes, international environmental law, the law of State responsibility, international human rights law, and the law of treaties.  She has also advised sovereign States, State-owned entities, and private entities on the law of sovereign immunity and the recognition and enforcement of arbitral awards under English law.  In addition, Oonagh has represented clients in international commercial arbitration proceedings conducted under ICC, LCIA, SCC and UNCITRAL Rules, as well as multiple domestic proceedings before English and US federal courts.

Oonagh has taught aspects of international law of the sea on a Master’s programme at King’s College London and speaks regularly on public international law and investment treaty arbitration. In May 2020, the American Society of International Law appointed Oonagh to serve on its Program Committee, alongside prominent US academics and international law practitioners.  Oonagh has served on ASIL’s Steering Committee for its signature topic, “Beyond National Jurisdiction: Human Activities in the Oceans, Polar Regions, Cyberspace and Outer Space”, following her elected tenure as Co-Chair of the Space Law Interest Group. In 2016, Oonagh was recognised by the Irish Times for women’s influence in global public affairs.

Prior to joining Fietta, Oonagh worked at major law firms in Washington DC and London. Oonagh has worked for the United Nations Office of Legal Affairs in New York, the European Commission in Brussels, and the Institute of International Economic Law at Georgetown University Law Center in Washington DC.



Fietta LLP, counsel (2020 onward), senior associate (2018-2020), consultant (2017-2018); Foley Hoag LLP, associate and senior associate (2011-2017); United Nations, Office of Legal Affairs, researcher (2010); Matrix Chambers, research assistant to Prof. Philippe Sands QC (2009-2010); King & Wood Mallesons, trainee and associate (2004-2009); Center for Strategic & International Studies, research assistant (2003-2004); Georgetown University Law Center, Institute of International Economic Law (2003); European Commission (2003)


English (native), French and Spanish


Solicitor-Advocate in England & Wales (Higher Courts Civil Proceedings) (2022)

Admitted to practise in the District of Columbia, USA (2014)

LLM Public International Law (2009-2010), University College London

Admitted to practise in England & Wales (2006)

Admitted to practise in the State of New York, USA (2005)

LLM General Legal Studies (2002-2003), Georgetown University Law Center

Postgraduate Diploma EC Competition Law (2001-2002), King’s College London

French Civil Law (1999-2000), Université de Bourgogne

LLB (Jt. Hons) Common & Civil Law with French (1997-2001), Queen’s University Belfast

Lawyer Rankings

London > Dispute resolution > Public international law

(Rising stars)

Oonagh SandsFietta LLP

The strongest PIL boutique in London‘, Fietta LLP has ‘vast experience in PIL matters‘. Dedicated to PIL and international arbitration work, the practice is routinely instructed by sovereign clients in their most sensitive PIL matters globally; and in contentious work, the team represents both investors and respondent states in investment arbitration. With ‘remarkable knowledge of PIL‘, founding partner Stephen Fietta KC regularly acts for sovereign states in high-profile territorial disputes; and Jiries Saadeh, ‘an absolute star of his generation‘, represents state and investor clients in international investment treaty cases. At counsel level, Australian lawyer Ashique Rahman is a founding board member of the Young Public International Law Group, a network of PIL practitioners; and Laura Rees-Evans and Oonagh Sands also both assist with complex PIL issues.

London > Dispute resolution > International arbitration

Boutique law firm Fietta LLP houses a dedicated international arbitration and public international law (PIL) practice that is widely respected for its investment disputes credentials. The ‘strategicStephen Fietta KC is regularly instructed by sovereign states to act in highly sensitive PIL matters, including some of the world’s highest profile territorial claims; and Jiries Saadehhas vast experience in investment disputes‘. Ashique Rahman is a partner as of July 2022, while Laura Rees-Evans and Oonagh Sands are the counsels to note.