Mr Sean O'Donnell > ByrneWallace LLP > Dublin, Ireland > Lawyer Profile

ByrneWallace LLP
88 Harcourt Street
Saint Kevin's
DO2 DK18

Work Department

Litigation and Dispute Resolution


Partner, Litigation and Dispute Resolution


Sean is a partner in the ByrneWallace LLP Litigation & Dispute Resolution Team.

He has a background in criminal law and has significant experience in acting for and dealing with regulatory bodies. Seán is experienced in the area of regulatory prosecutions and has defended cases brought by many state regulators including the Environmental Protection Agency and the Health and Safety Authority.  Seán prosecutes various offences for the Health Service Executive and is an experienced advocate in the District Court. Seán has represented and advised persons of interest in investigations and inquiries.

Seán advises corporate clients in relation to Data Protection Law and in particular in relation to Data Access Requests and Data Security Breaches.

Seán advises state bodies in relation to their powers and functions and has advised on  investigating complaints and investigating alleged offences. He has also advised on the redrafting of regulations.

He has advised directors of companies in relation to their exposure in regulatory and criminal investigations. He has also advised on search warrants and advised a private client in relation to a dawn raid by the Competition and Consumer Protection Commission.


  • Association of Regulatory Lawyers
  • The Law Society of Ireland
  • Dublin Solicitors Bar Association


  • Certificate in Data Protection Practice, Law Society of Ireland, 2015
  • Advanced Diploma in Juvenile Justice, Honourable Society of Kings Inns, 2014
  • Certificate in Healthcare Law and Practice, Law Society of Ireland, 2013
  • Advanced Diploma in Corporate, Regulatory and White Collar Crime:  Honourable Society of Kings Inns, 2012
  • CEDR Mediation Advocacy Certificate, 2010
  • Professional Qualification as Solicitor; Law Society of Ireland, 2006
  • Law and European Studies (L.L.B), University of Limerick, 2002

Lawyer Rankings

Ireland > Data privacy and data protection

ByrneWallace LLP advises both public and private sector clients on a range of day-to-day data privacy and protection matters and assists with responding to issues such as data breaches and changes to regulations. The team also acts alongside the firm’s corporate practice to handle the data-related aspects of M&A transactions and provide advice on commercial matters including outsourcing agreements. Sean O’Donnell leads the team, while Zelda Deasy, who was promoted to partner in December 2021, is another key contact.

Ireland > Public sector

(Next Generation Partners)

Sean O’DonnellByrneWallace LLP

The public sector practice at ByrneWallace LLP is notable for its breadth, providing comprehensive advice to public bodies on their operations. Practice head Michelle Ní Longáin specialises in employment law, and is particularly active in advising public sector clients on protected disclosure law. The team also represents clients in litigation, including judicial review proceedings, with Jon Legorburu a key figure in contentious work. Health and social care is a particular sector of focus for the practice; Sinéad Kearney and Olive Doyle specialise in this area. Litigator Sean O’Donnell handles regulatory enforcement proceedings and is also engaged by clients to advice on the response to cyberattacks.

Ireland > Information technology

ByrneWallace LLP is highly active in advising on M&A transactions involving companies in the IT sector and also acts for these companies in fundraising rounds. Data privacy is another area of focus for the team, with Sean O’Donnell leading on this work. Darren Daly serves as practice head.

Ireland > White-collar crime

In addition to representing clients facing investigations and prosecutions, ByrneWallace LLP‘s white-collar crime practice is noted for its expertise in advising regulatory bodies on the exercise of their powers and the drafting of documents and submissions, as well as representing regulators in litigation. Elsewhere, the team is frequently instructed by the victims of white-collar crimes such as cyber breaches and organisations that are not accused of wrongdoing but are drawn into regulatory investigations. The team is jointly led by commercial litigator Jon Legorburu and Sean O’Donnell, who has deep experience of acting for public sector clients.

Ireland > Dispute resolution

ByrneWallace LLP remains best known for contentious matters involving public sector bodies, including those in the health, education and tourism sectors. Jon Legorburu leads the team and has an impressive history in commercial litigation and public sector disputes. Mona Costelloe is another senior name with extensive expertise in real estate disputes, regulatory enforcement matters and more general commercial litigation. Sean O’Donnell is also noted for contentious regulatory work, and Mark O’Shaughnessy is a growing force in the market. Valerie Hourigan is rated for real estate and procurement disputes.