Matheson LLP

Partner in the Tax Department

Mark O’Sullivan is a partner in the firm’s Tax Department and advises on all aspects of Irish corporate taxation.  His primary focus is advising overseas clients establishing operations and doing business in and through Ireland.  Mark also advises extensively on all aspects of international tax planning, including IP planning, cross-border reorganizations and financing transactions.

Mark was previously seconded to the legal department of a large investment bank in London in 2004.  Mark was based in the firm’s Palo Alto office from 2007-2020 and now splits his time between Dublin and Palo Alto.

Mark is a vice-chair of the Foreign Lawyer’s Forum of the Tax Section of the American Bar Association (ABA), and is also actively involved in the International Fiscal Association (IFA). Mark regularly speaks on international tax issues and has also published articles in Tax Notes International, the International Tax Review, the Irish Taxation Review, IFLR, BNA and Finance Magazine.  Mark has also guest lectured on international tax matters at the University of Washington and San Jose State University.

Law Society of Ireland

University College Dublin and Université de Toulouse I (France), (Bachelor of Civil Law)

University College Dublin, (Diploma in Financial Services Law)

AITI / Chartered Tax Adviser (CTA)