Admitted to the Paris bar and the Supreme Court of Queensland (Australia), William Ahern is an associate in the International Arbitration practice of the Paris office. He represents States, State entities, foreign investors and companies in investment treaty arbitration and international commercial arbitration.

Prior to joining Mayer Brown in 2013, William clerked for a Judge of the Federal Circuit Court of Australia and trained and qualified as lawyer in the litigation department of a large Australian commercial law firm.

In addition to his native English, William is fluent in French.

Spoken Languages

  • English
  • French


Investor-State Arbitration 

  • The Arab Republic of Egypt as respondent in an ICSID Arbitration initiated by a French multinational corporation with respect to a waste management services contract in a major Egyptian city (ICSID Case No. ARB/12/15)
  • Kuwaiti investors in an ICSID Arbitration against the Hashemite Kingdom of Jordan in a dispute related to the tax treatment of their investment (ICSID Case No. ARB/13/38)
  • A US investor and his US companies in an ICSID Arbitration against the Republic of Romania in a dispute related to the expropriation and treatment of their investments in the press distribution and real estate sectors (ICSID Case No. ARB/10/13)
  • A European company against a North African State in an UNCITRAL investor-State dispute on the basis of a bilateral investment treaty relating to the construction of a major infrastructure project in that country
  • The Republic of The Gambia in an ICSID Arbitration initiated by the subsidiary of a mining company in a dispute related to the termination of a mining license in that country including before an ad hoc Committee (ICSID Case No. ARB/09/19)
  • The Republic of The Gambia in two ICSID Arbitrations against a British oil company in a dispute related to the termination of concessions in off-shore fields in that country (ICSID Case No. ARB/14/16 and ICSID Case No. ARB/14/7)

Commercial Arbitration

  • A West African State in arbitration proceedings conducted under the Rules of the London Maritime Arbitrators Association in a dispute involving its European partner (and its Pacific Islands entity) in a Joint Venture agreement for transportation services
  • A French information technology company in a dispute against an Asian entertainment company under a contract providing for SIAC arbitration
  • A Middle-Eastern company against an North East Asian company in SIAC arbitration proceedings concerning a breach of contract in relation to the health sector in a Middle Eastern country
  • A Lebanese company in an ICC arbitration against a Dutch company concerning an intellectual property license agreement applicable in the Middle East, where the restitution of trademarks is sought
  • A Middle Eastern party against an Asian company in a pending ICC arbitration with respect to outstanding legal fees
  • A Middle Eastern food company in an ICC Arbitration against its Middle Eastern partner over the breach of their Joint Venture Agreement
  • A Middle Eastern company and A British Virgin Islands in and ICC arbitration, against US companies, in relation to a disputed construction contract in a North African State


Université Jean Moulin Lyon 3, LLM International and European Law (with honours)

College of Law, Brisbane, Australia, Graduate Diploma of Legal Practice

Queensland University of Technology, Bachelor of Laws

Queensland University of Technology, Bachelor of International Business


  • Paris
  • Australia, Queensland