Our Team

Mark O'Shaughnessy
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Mark is a litigation and regulatory investigations partner in ByrneWallace LLP.

Mark advises domestic and international organisations on complex disputes with a particular focus on corporate disputes, contentious intellectual property and insurance matters in the education, health, life science and TMT sectors.

He also has extensive experience in advising private, semi-state and public organisations in the context of regulatory investigations and enquiries. 

Reputation management is core to Mark's expertise and he has managed the corporate reputation strategies of numerous companies through times of crisis.

Mark has also been appointed by the European Commission as a member of its Expert Group against SLAPP (Strategic Lawsuits Against Public Participation).

Key Experience

  • Managing strategic corporate disputes for publically listed companies, multinational corporations and large Irish companies.
  • Advising businesses on contractual disputes, minority oppression actions and quasi-partnership disputes before the Commercial Court and High Court.
  • Acting for organisations in intellectual property disputes, particularly patent disputes and passing-off actions.
  • Advising on insurance policy interpretation and coverage with a particular focus on business interruption insurance, D&O insurance and environmental impairment liability insurance.
  • Advising organisations during internal investigations and managing external engagements with regulatory bodies and parliamentary committees. 
  • Advising domestic and international companies on protecting their corporate reputations both online and in traditional media.


  • Law and Accounting, University of Limerick, 2003
  • Admitted as a Solicitor, Law Society of Ireland, 2008
  • Diploma in Commercial Litigation, Law Society of Ireland, 2009
  • Professional Diploma in Arbitration, University College Dublin, 2011


  • Law Society of Ireland
  • Law Society of England and Wales
  • Dublin Solicitors Bar Association
  • Arbitration Ireland
  • British Irish Commercial Bar Association


'Mark O'Shaughnessy's clarity, tenacity and diligence never dull his empathy. His collegiate humanity is a real differentiator. I feel real gratitude to have journeyed with Mark and his team.' – Legal 500, 2024

'Mark O'Shaughnessy - always very strong strategic and commercial legal advice, sees the issue from many angles. Mark is also very practical and easy to understand, he always is available and keeps meetings focused and on point. He is also easy to get along with, and very personable.' – Legal 500, 2024

'Mark O'Shaughnessy is an outstanding leader in the field, always operating at the cutting edge of new developments. He is a genuine expert in a complex and evolving field and has an impressive ability to synthesise and communicate the law effectively. He has invaluable experience in managing external engagements with regulatory bodies and parliamentary committees.' - Legal 500, 2024

'Mark O'Shaughnessy in particular is always available, sources particular requirements, expert witnesses, is well-versed on data protection and articulate and engaging when engaging with third parties on our behalf.' – Legal 500, 2024

'Mark O'Shaughnessy is generous with sharing his legal expertise with colleagues and is a skilled communicator.' - Legal 500, 2024

'Mark O’Shaughnessy demonstrated relentless commitment, energy and confidence throughout. This rare combination shored up our energy when we most needed it.’ – Legal 500, 2023

'Mark O’Shaughnessy is a leading expert in the fields of media and technology law, his knowledge of these constantly evolving areas is impressive, and his ability to present developments in the law in a clear and concise way is of great assistance. He has the ability to identify practical pathways and solutions to overcome difficult legal issues faced by clients in these areas.’ – Legal 500, 2023

‘Mark O’Shaughnessy was excellent. He was fully on top of his brief, had clearly researched in advance of calls and meetings and although our industry is a niche one, we didn’t have to waste valuable time bringing him up to speed. There was a need for a quick turnaround on some material and documents and this happened seamlessly and efficiently and to a very high standard.’ – Legal 500, 2022

‘Mark O’Shaughnessy has a very strong ability to communicate effectively. He is very engaged and comfortable with the subject matter of social media and the law. Mark is accessible and very pleasant to work with.’ – Legal 500, 2022

‘Mark O’Shaughnessy has been an exceptional support on an extremely difficult, contentious and time-limited matter. He demonstrated exemplary practical knowledge and awareness in guiding us through a difficult matter. I would have no hesitation in recommending the work of him and his team.’ – Legal 500, 2022

‘Mark O’Shaughnessy is the primary contact and his ability to understand thoughts, provide practical yet strategic advice is exemplary. He is also ultra transparent in all dealings, and even working remotely in no way impacted on service.’ – Legal 500, 2022

‘My main point of contact is with Mark O’Shaughnessy and I find him very efficient to deal with. He’ll put you in touch with the appropriate person depending on our issue. He understands the importance of value for money in a NFP organisation and they always do their best fees wise. I always get a feeling they genuinely want to help and protect us as best they can.' – Legal 500, 2022

‘Mark O’Shaughnessy is smart, emotionally committed and very inspiring.’ – Legal 500, 2021

‘I found Mark O’Shaughnessy to be excellent in all respects. I felt he was exceedingly engaged and energised by the matter and was wholly committed to our interests. I found this level of commitment to be quite different from other legal engagements where the client is sometimes made to feel to be nuisance in a busy day of other, more important matters.’ – Legal 500, 2021

‘We are involved in a number of cases to protect the business and to manage reputational risk. These are being litigated in the High Court currently. We are using the services of Mark O’Shaughnessy, who has an excellent legal mind and who is highly responsive to client needs in the area of defamation. This is a new area of litigation for the business and Mark is very strong at ensuring complex legal matters are explained in clear and concise language so that the business can make informed decisions in terms of strategy and tactics.’ – Legal 500, 2021

‘I have also worked with Mark O’Shaughnessy who is top-class in the area of copyright law.’ – Legal 500, 2021

‘Referred to the Intellectual team we were delighted to meet Mark O’Shaughnessy and his team and were comforted by their grasping of the matter, their ability to communicate complex legal concepts and their ability to clearly strategise the most efficient path to manage the threat. I would commend their capacity to communicate the complex in a clear and productive style.’ – Legal 500, 2021