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Calum Warren is a partner in the Competition and Regulation Group.  Prior to joining Matheson, Calum worked at leading international law firms in Brussels and London.

Calum advises on all aspects of Irish and EU competition and regulatory law including merger control, competition compliance and investigations, sector regulation, public procurement, state aid and general EU law.  Calum has also gained in-depth experience in a range of sectors including financial services, telecommunications and media (TMT), agri-business, energy, manufacturing, healthcare, food & beverages and transport. 

Calum specialises in advising on and managing clearance strategies for M&A transactions before the Competition and Consumer Protection Commission (CCPC) and the European Commission, including transactions subject to in-depth Phase 2 investigations and remedies negotiations.  His previous roles in Brussels and London also enable Calum to bring considerable multi-jurisdictional perspective to his advice.

Calum also specialises in managing competition investigations before the CCPC and the European Commission, including representation during on-site inspections (‘dawn raids’), whistle-blower applications and follow-on litigation before the Irish and EU courts.  Calum also has significant expertise in advising on competition compliance issues, including competitor collaborations, the competition aspects of distribution arrangements and technology transfer / IP arrangements and internal compliance programmes (including ‘dawn raid’ preparedness). 

Calum contributes articles to leading international legal publications and speaks regularly on EU competition issues.


  •  Advising a party involved in the Irish Competition and Consumer Protection Commission’s (CCPC) private motor insurance investigation.
  • Advising clients involved in M&A transactions subject to complex merger reviews including Phase 2 reviews before the CCPC and the European Commission.
  • Advising various international clients on various Irish competition regulators (including the CCPC and the Commission for Communications Regulation) and European Commission investigations and information requests regarding competition law compliance, regulatory breaches and State aid complaints.
  •  Whistle-blower applications to the CCPC / Director of Public Prosecutions for immunity against prosecution for Irish competition offences.
  •  EU law adviser to companies subject to audits by EU agencies, including audits of grant funding by the European Commission and OLAF.
  •  Advising a multinational investment bank on its participation in a European Commission investigation into alleged anti-competitive conduct, including advising on related regulatory considerations vis-à-vis the UK Financial Conduct Authority*.
  •  Advising on dawn raids by EU and other national regulators, including attending a 2015 national regulator raid of a media advertising business in the UK and advising on identifying and mitigating risk after the raid*.
  •  Advising a multinational conglomerate on multiple European Commission competition law investigations and appeals against European Commission fining decisions before the EU courts, including a successful appeal against the European Commission’s CRT fining decision leading to a €28 million reduction in fines*.
  •  Advising on State aid issues associated with obtaining State funding for clients, including in crisis situations and through obtaining European Commission approval*.
  • Providing competition law compliance and dawn raid training to multiple clients, including dawn raid simulation exercises.
Calum Warren provides excellent advice, is very solution focused and practical, as well as being incredibly responsive. All very valuable when trying to address complex issues in a commercial environment.

EU and Competition: The Legal 500 2023

Calum Warren is excellent, very practical, excellent availability and he explains complex topics very clearly.
EU and Competition: The Legal 500 2023


Qualified as a solicitor in Ireland 

King’s College, London (Post-Graduate Diploma in Economics for Competition Law)

Ludwig-Maximilians-Universität (LMU), Munich (LL.M. in European and International Business Law)

Trinity College Dublin (LL.B. in Law and German)