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Oonagh Sands

Fietta LLP


Oonagh Sands is a dually-qualified English and US-lawyer.

She has significant experience representing sovereign States and their State-owned entities, as well as private individuals and 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. In addition, Oonagh has counselled States on the law of sovereign immunity, territorial and maritime boundary disputes, as well as issues arising under the law of the sea. In 2018, The American Society of International Law appointed Oonagh to serve on the steering committee for its signature topic “Beyond National Jurisdiction: Human Activities in the Oceans, Polar Regions, Cyberspace and Outer Space”, following her tenure as elected Co-Chair of the Society’s ‘Space Law Interest Group’.

Prior to joining Fietta, Oonagh worked at major law firms in Washington DC and London. Oonagh has also 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.

She speaks French and Spanish.

In 2016, Oonagh was recognised by The Irish Times for women’s influence in global public affairs.



Fietta LLP, senior associate (2018 onward), consultant (2017-2018); American Society of International Law, co-chair, Space Law Interest Group (2016-2018); 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


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

London: Dispute resolution

International arbitration

Within: International arbitration

Fietta LLP 'has a large case load and has talent from top to bottom'. The firm is widely respected for its experience in investor-state arbitration. Stephen Fietta QC, who took silk in 2019, has secured numerous substantial awards for his state and investor clients; Jiries Saadeh and Ashique Rahman were promoted to partner and counsel, respectively. Oonagh Sands and Laura Rees-Evans are the senior associates to note.

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Public international law

Within: Rising stars

Oonagh Sands - Fietta LLP

Within: Public international law

Arguably, 'one of the leading boutique practices in public international law', Fietta LLP has substantial expertise in investment treaty proceedings, maritime boundary disputes and human rights matters. The practice is regularly instructed by sovereign states, corporate, individual and NGO clients across a wide spectrum of public international law matters. Stephen Fietta QC has 'an outstanding reputation' in investment treaty arbitration and often leads on high-profile and substantial claims, including acting for a large group of Greek investors in an ICSID arbitration against the Republic of Cyprus arising from the Cypriot financial crisis and European Union/IMF bail-out of 2013. Also of note are recently promoted partner Jiries Saadeh, counsel Ashique Rahman and associates Oonagh Sands and Laura Rees-Evans.

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