Dr. Daniel G. Costelloe

Daniel Costelloe is counsel in the Litigation/Controversy Department and is a member of the International Arbitration Practice Group. Dr. Costelloe focuses his practice on international arbitration matters across a range of industries, including oil and gas, financial services, manufacturing and automotive. He has represented clients in arbitrations under a variety of arbitral rules and has particular experience with the ICSID, ICSID Additional Facility, LCIA, UNCITRAL and ICC arbitration rules. Recent highlights include representing investors in investment-treaty claims against eastern European states and representing a government in a contractual dispute with upstream oil and gas investors. He also advises clients on public international law matters and in arbitration-related court proceedings.

Dr. Costelloe also acts in pro bono matters. Highlights include working with the Media Legal Defence Initiative on a challenge before the East African Court of Justice to a national law's compatibility with a state's treaty obligations and on an application to the European Court of Human Rights.

Dr. Costelloe publishes on various topics within the field of public international law, including the law of treaties, international responsibility and state succession. He has taught undergraduate supervisions in public international law at Cambridge University and guest classes on the law of treaties at Queen Mary University of London, and he regularly speaks at conferences and expert seminars on current issues in international law.

Professional Activities

  • American Society of International Law
  • Chatham House, Royal Institute of International Affairs


Insights & News


  • Education

    • PhD, Law, University of Cambridge, 2014

      WM Tapp Studentship in Law, Managing Editor and Blog Editor, Cambridge Journal of International and Comparative Law
    • LLM, Harvard Law School, 2010

      Line Editor, Harvard International Law Journal
    • LLB (Law with French Law), University College London, 2009

      first class Andrews Medal, Hurst Prize, Richardson Prize
  • Admissions

    • New York

  • Languages

    • German

    • French