Our Team

Sean O'Donnell
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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. 


  • Successfully defended large manufacturing company in a Health and Safety prosecution which was ultimately struck out by the Court.
  • Represented, advised and attended interviews with clients in the context of investigations by the Office of Director of Corporate Enforcement and the Health and Safety Authority and An Garda Síochána.
  • Advised an Irish Tourism organisation on the redrafting of regulations in relation to hotels.
  • Advising an Irish Tourism organisation on its enforcement powers under its statutory regime.
  • Advises and represents a leading body in the Irish Healthcare sector in regulatory enforcement proceedings (prosecution and civil enforcement) in the District and Circuit Court.
  • Advised public body on the General Block Exemption Regulation in relation to the provision of State Aid.
  • Advised and represented several private and public organisations in dealing with Data Access Requests and Data Security Breaches. 


  • 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


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


'Sean O'Donnell is very wise and informed. Very practical.' - Legal 500, 2024

'Mona Costelloe and Sean O'Donnell are excellent litigators, who are working on novel areas of data protection law.' - Legal 500, 2024

‘Sean O’Donnell provides excellent and calm advice to his clients. His expertise in dealing with criminal matters gives him a valuable advantage in addressing issues in this area. He also has excellent interpersonal skills to guide clients through the issues they face with white-collar crime matters.’ - Legal 500, 2023

‘Seán O’Donnell is a true professional. He is always available for any urgent or last-minute meetings. He has an excellent communication style, pays great attention to detail and will always develop bespoke legal solutions for clients in respect of complex legal scenarios. Sean has also demonstrated his unique ability to traverse through new significant data protection investigations in the area of cyber security.’ - Legal 500, 2023

‘Sean O’Donnell and Eimear Redmond are particularly helpful. Sean is very responsive to queries and requests, and they both take time to explain their rationale.’ - Legal 500, 2023

Sean O’Donnell is ranked Next Generation Partner by Legal 500, 2023

‘Sean O’Donnell provides expert practical advice, drawing on significant experience working on some of the most complex data protection issues in the jurisdiction in recent years.’ - Legal 500, 2022

‘We have dealt with Sean O’Donnell and found him also to have a very high level of expertise, very good availability and a clear business understanding. All the associates have been very knowledgeable and great to deal with.’ - Legal 500, 2022

‘Attention to detail particularly from Sean O’Donnell was second to none, especially when it came to the important time towards the end of the case.’ - Legal 500, 2022

Seán O’Donnell is a safe pair of hands on all matters. - Legal 500, 2022

Sean O’Donnell is a safe pair of hands. - Legal 500, 2021

Sean O’Donnell is approachable and responsive. - Legal 500, 2021

Seán O’Donnell has extensive experience of advising and representing clients in white-collar crime situations and related areas.‘ - Legal 500, 2020

We regard Seán O’Donnell as a leading figure in the area of white-collar crime. His practical advice cuts to the chase in what can be complex regulatory areas. - Legal 500, 2020

Seán O’Donnell is a very hands-on and knowledgeable lawyer who provides clear and unambiguous advice. - Legal 500, 2020

Seán O’Donnell is client and delivery focused. - Legal 500, 2020

Seán O’Donnell is proficient, engaged and highly responsive. He is also an unusually good listener and an excellent strategist. I couldn’t rate him more highly. - Legal 500, 2020

The ‘calm and very thorough’ O’Donnell has significant experience in defending individuals in criminal investigations, and was active on behalf of corporates and individuals in defending alleged frauds. - Legal 500, 2018