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Katelyn Horne advises sovereign States, State-owned entities, private companies, and prominent individuals in relation to international arbitration, public international law, and other disputes. She represents sovereign States in investment treaty arbitrations concerning a variety of industries and economic sectors, including national infrastructure, oil and natural gas, banking and financial institutions, and intellectual property. She also provides counsel to sovereign States with respect to maritime boundaries and entitlements, sovereign immunity, and international human rights law; represents private entities in international commercial disputes; and advises individuals on issues of sovereign and diplomatic immunity. Her experience includes disputes brought before international tribunals (administered by various arbitral institutions), the International Court of Justice, the United Nations Human Rights Committee, and the United Nations Working Group on Arbitrary Detention. She also has experience in US litigation.

Prior to joining the firm, Ms. Horne served as an associate legal officer to His Excellency Judge Hisashi Owada of the International Court of Justice in The Hague. She received the David M. Berger Memorial Prize in International Law and was a member of Columbia Law School's two-time national championship Jessup International Law Moot Court team. Ms. Horne previously served in the Executive Branch of the US Government, including as a political appointee at the US Department of Homeland Security and in positions at the White House, the US Department of State, and the Office of the US Trade Representative.


  • Representing a sovereign State with respect to its maritime entitlements and the application of the United Nations Convention on the Law of the Sea.
  • Representing the Republic of Peru in an investment dispute concerning critical infrastructure for gas transportation.
  • Representing the Republic of Peru in an investment dispute concerning the exploration and exploitation of natural resources in the Amazon.
  • Representing the Republic of Bulgaria in an investment dispute with a major corporate commercial bank.
  • Representing the Republic of Colombia in two investment disputes concerning financial institutions and the banking sector.
  • Representing the Republic of Panama in an investment dispute concerning intellectual property rights.
  • Representing the Republic of Chile in the long-standing Pey Casado arbitration.
  • Representing the Republic of the Philippines in an investment dispute concerning a natural gas development project.
  • Representing a major Korean financial institution in a dispute with American investors.
  • Representing two Korean technology companies in a dispute regarding technology license agreements.
  • Representing two Peruvian energy companies in a dispute concerning its supply chain for liquified natural gas.
  • Representing a Bulgarian State-owned entity in a dispute regarding the electric power grid.
  • Representing an American technology company in a dispute with a Korean commercial partner and distributor.
  • Representing a South American railway concession in a dispute with its shareholders.


Arnold & Porter Secures Another Complete Victory for Republic of Peru in International Arbitration
Arnold & Porter Achieves Significant International Arbitration Victories for Republic of Peru
Status Report on Principles of International and Human Rights Law Relevant to Climate Change
Sabin Center for Climate Change Law
Role of International Courts during Armed Conflicts
Moderator, Harvard International Arbitration Conference
The Time Has Come to Prohibit Double Hatting
Investment Treaty Arbitration and International Law, Vol. 14


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  • J.D., Columbia Law School, 2015, James Kent Scholar
  • B.S.F.S., International Politics, Georgetown University School of Foreign Service, 2011, magna cum laude


  • District of Columbia
  • North Carolina

Government & Military Service

  • Confidential Assistant, US Department of Homeland Security (2012)
  • Associate, Executive Office of the President, The White House (2010-2011)


  • International Court of Justice, His Excellency Judge Hisashi Owada


  • Member, American Society of International Law