Leonidas Theodosiou focuses his practice on UK, EU, and international antitrust/competition matters and competition litigation. Leo has practiced in London and Brussels for nearly a decade, representing multinational firms in merger control proceedings, litigation in the English and EU Courts, as well as enforcement matters, including cartel, abuse of dominance, and state aid investigations. He is admitted to practice in England & Wales (Solicitor), the EU, and New York.
Leo is a partner in Morgan Lewis’ “Highly Commended” competition team in London (The Lawyer Awards, 2021, 2022). He advises on all aspects of UK and EU competition law and competition litigation.
Leo is recommended by The Legal 500 UK for both EU and Competition and Competition Litigation. In relation to competition litigation, Leo is “noted for his extensive international capabilities” and praised for being “extremely skilled and responsive, and [for] bring[ing] a real depth of experience in this complex and challenging area.” In relation to transactional matters, clients say he offers “excellent support and is always on hand during a transaction to offer top class insights which allow for clear and fully informed decision making.”
Prior to joining Morgan Lewis, Leo spent several years as an antitrust associate with a Magic Circle law firm, resident in Brussels. In 2018, Leo was seconded to Tata Steel—one of the world’s largest steelmakers—where he served as the organization’s in-house counsel dedicated to antitrust.
Leo speaks regularly at seminars and conferences and contributes frequently to leading academic and professional publications; one of his recent articles on EU state aid control was nominated as best business article at the 2020 Concurrences Antitrust Writing Awards. He is often quoted by the Global Competition Review and other leading specialist publications on current competition law issues.
In 2021, Leo was featured in the Festival of Talent edition of The Lawyer for his contribution in securing Sainsbury’s victory in the UK Supreme Court in its interchange fee litigation against Visa. He is a member of the Morgan Lewis team which was awarded Behavioural Matter of the Year—Europe, Challenges to CMA Search Warrants by Global Competition Review (2018).
Leo holds post-graduate degrees in law from Harvard Law School and the University of Cambridge (Trinity Hall). He has received significant awards and fellowships in recognition of his research and academic achievements, including a Fulbright Fellowship by the US Department of State, and was selected to deliver the 2013 Commencement Speech at Harvard Law School.
Leo is the incoming Vice Chair of the American Bar Association’s Privacy and Information Security Committee. He speaks and writes frequently about data protection issues, in particular in the context of M&A transactions.
Competition Litigation
Merger & FDI Control
Antitrust Investigations
State Aid Control
Recommended, Corporate and Commercial: EU and Competition, The Legal 500 UK (2023)
Recommended, Dispute Resolution: Competition Litigation, The Legal 500 UK (2023)
Vice Chair, ABA Committee on Privacy & Information Security
Highly Commended, Competition Team of the Year, The Lawyer Awards (2021, 2022)
Member, Behavioural Matter of the Year—Europe, Challenges to CMA Search Warrants, Global Competition Review (2018)
Member, Practice Group of the Year, Competition, Law360 (2017–2021)
Member, Law Society of England and Wales (Competition Section)
Fulbright Fellow, US Department of State (2012–2013)
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