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Clare O’Brien


Clare is Life Sciences Sector Lead and regularly advises major US and international clients on their public and private mergers and acquisition transactions, including public company restructurings, joint ventures and large public transactions.

She also provides counsel on corporate law questions, including corporate governance matters.

Prior to joining the firm, Ms. O’Brien worked with the law firm of Brady & Tarpey, P.C., where her practice included cross-border corporate transactions, litigation and domestic relations. She began her legal career at the Irish law firm of Eugene F. Collins & Son.


Representative matters

Mubadala Capital, established as the financial investment arm of Mubadala Development Company, in various transactions, including its 2022 acquisition of Canada Cartage Corporation and its recently completed acquisition, together with members of Fortress management, of all of the indirect interests in Fortress Investment Group LLC.

Mubadala Investment Company, a public joint stock company wholly owned by the Government of the Emirate of Abu Dhabi, in various transactions, including its global business partnership with General Electric Company, its investment in the EBX Group (and related restructuring transactions), its investment with Trafigura Pte. Ltd. In MMX Porte Sudeste and in connection with the establishment of several private lending programs with global financial institution origination partners, which provide financing solutions to U.S. and European middle-market businesses.

Ardagh Group in various transactions, including its US$8.3 billion “de-SPAC” transaction involving the combination of its metal packaging business with Gores Holdings V, Inc., a special purpose acquisition company, the combination of its Food & Specialty Metal Packaging business with the packaging business of Element Holdings II L.P., an entity controlled by The Ontario Teachers' Pension Plan, to form Trivium Packaging, its acquisition of certain metal beverage can manufacturing assets from Ball Corporation and Rexam PLC with an enterprise value of $3.42 billion, and its sale of Anchor Glass Container Corporation to an affiliate of KPS Capital Partners LP.

Boston Scientific Corporation in various transactions, including its pending acquisition of Axonics Inc., a publicly traded MedTech company, for approximately $3.7 billion, its 2022 acquisition of Apollo Endosurgery, Inc., a Delaware public company, its acquisition of Baylis Medical Company, a privately held Canadian company, its acquisition of BTG plc, a public company organized under the laws of England and Wales, its acquisition of the men's health and prostate health businesses of Endo International plc, the sale of its neurovascular business to Stryker Corporation, its acquisition of and the restructuring of its interests in Advanced Bionics Corporation, its acquisition of Guidant Corporation, the sale of Guidant's vascular businesses to Abbott Laboratories and in various corporate and other transactional matters.

Atrion Corporation in its pending acquisition by Nordson Corporation for an aggregate equity value of approximately $815 million.

Raytheon Company in various transactions, including its 2020 “merger of equals” combination with United Technologies Corporation.



Leadership Positions And Professional Affiliations

Member of the Board of Directors of The French American Foundation and Foundation Merieux USA and a trustee of Berwick Academy, Maine
Clare O'Brien utilizes her extensive experience in corporate transactions to assist a client base of significant public and private companies. She regularly handles M&A, joint ventures and corporate governance issues.
Chambers USA, 2023


  • Leading Lawyer Legal 500 M&A/Corporate and Commercial: M&A: Large Deals ($1BN+) 2021, 2022, 2023
  • “Dealmaker of the Year” by The American Lawyer, 2021
  • Top U.S.A. Women Dealmaker by the Global M&A Network 2021
  • Top Women in Dealmaking The Deal 2021, 2022, 2023



New York State, 1986


Irish Roll of Solicitors


B.S., Univ of Dublin Trinity College, 1982

J.D., Ireland (Incorp. Law Soc. Of), 1985

A&O Shearman was formed on May 1, 2024 by the combination of Shearman & Sterling LLP and Allen & Overy LLP and their respective affiliates (the legacy firms). Any matters referred to above may include matters undertaken by one or more of the legacy firms rather than A&O Shearman.