John O’Leary


John is a Partner in our Dispute Resolution team. He specialises in domestic and multi-jurisdictional contractual, tortious, professional negligence and shareholder disputes. 

John frequently acts for financial institutions in complex commercial disputes and he has also acted for both claimants and respondents in domestic and international commercial mediations. 

John also has extensive experience in advising clients involving funds litigation. Most notably, John represented SPV OSUS in respect of losses suffered by Optimal Strategies U.S. Equity Limited following the collapse of the Madoff Ponzi scheme with an overall claim value of €3bn.


  • Commercial Litigation
  • Insolvency
  • Professional Negligence Claims

Representative Matters

  • Acted for Aer Lingus Limited against the daa in respect of losses that Aer Lingus incurred due to failures of a baggage system at Dublin Airport in 2017.
  • Acted for a major financial institution in carrying out an independent review culminating in a report which was lodged with the Financial Regulator.
  • Represented Valero Energy Ireland Limited in a breach of contract dispute against Applegreen.


Legal 500, 2020:

"John O’Leary is very capable, intelligent and professional".  

  • LinkedIn

Areas of Expertise

Restructuring & Insolvency Dispute Resolution

Professional Memberships

Law Society of Ireland


University College Dublin, BBLS

Smurfit School of Business, MBS