Tadhg O’Leary

Tadhg is a Counsel at Signature’s London office, with extensive experience in complex, high-value litigation, international arbitration, investigations and advisory matters.

With over a decade of experience Tadhg’s practice covers commercial litigation at all court levels – High Court, Court of Appeal and Supreme Court – international arbitration, particularly under LCIA, ICC and LMAA rules, and investment treaty arbitration. His experience also includes civil fraud, corporate disputes (including SPA disputes, JV disputes, post-M&A matters) and competition law / antitrust disputes

Tadhg represents private companies and high-net-worth individuals from across the globe including Europe, the Middle East, Asia and Africa). He advises clients from a wide range of industry sectors, such as commodities, energy, finance, manufacturing, shipping, technology, telecommunications.

Tadhg has been ranked as a ‘Recommended Lawyer’ in The Legal 500 UK 2025 Guide for his civil fraud practice, with the Guide noting that he “regularly acts in high-stakes fraud claims.”

Prior to joining Signature Litigation, Tadhg trained and qualified at international law firm, Allen & Overy (as it then was), during which time he also spent time seconded to Allen & Overy’s Paris and Hong Kong offices.

Tadhg speaks professional-standard French and is also qualified in the Republic of Ireland.

Commercial Litigation

Representing Privinvest, a world leader in naval shipbuilding, in a USD 3.1bn high-profile, complex Commercial Court claim (now on appeal to the Court of Appeal) brought by the Republic of Mozambique against Credit Suisse, Privinvest, and others. The claim relates to supply agreements and supporting financial instruments and guarantees entered into by state-owned enterprises dedicated to the development of Mozambique’s offshore Exclusive Economic Zone and supporting international investment into its oil and gas reserves. The claim engages allegations of bribery of Mozambican government officials. An appeal on issues of sovereign immunity featured in The Lawyer’s Top 10 Appeals of 2024. Following judgment against Privinvest (though in which most of Mozambique’s allegations failed), Privinvest obtained permission to appeal on numerous grounds, including on whether a fair trial was possible in light of established disclosure breaches by Mozambique. The appeal is listed to be heard by the Court of Appeal in June 2026.
Representing Renault and certain of its Authorised Dealerships in the NOx Diesel Emissions Group Litigation in London, a claim of unprecedented scale in the English court, in which more than 1.6 million claimants have issued claims against car manufacturers (and others). The case involves a 12-week technical trial which started in October 2025 and will conclude in March 2026.
Representing a HNW individual in cross contribution proceedings against a co-defendant arising out of the settlement of a high-profile conspiracy claim for USD 350m brought by a global fishing company. We also provided strategic advice on the global litigation strategy which involved civil and criminal actions in Europe and Asia.
Representing an investment manager in a EUR 580m complex joint venture dispute with a major Canadian technology company regarding a series of energy projects.
Representing an international bank in disputes with a large number of ship owners and charterers (over 800 LMAA arbitrations and court proceedings worldwide and almost 200 vessel arrests) arising out of the bankruptcy of a large marine bunker supplier, including an expedited test case in which the client succeeded before the arbitral tribunal, the English High Court, Court of Appeal and Supreme Court.
Competition damages claims, including:
- representing global technology company in defending a EUR 667m claim regarding computer monitors, in which the client successfully challenged the High Court’s jurisdiction (later overturned by the Court of Appeal) before continuing to defend the claim until later settled;
- representing a global technology company in defending an EUR 1.8bn damages claim regarding mobile phone batteries, in which the client successfully challenged the High Court’s jurisdiction and subsequently defend new proceedings brought by way of a Finnish arbitration; and
- representing a large European manufacturer of foam products in three separate foam cartel damages proceedings.
Representing an international banking group in a large currency swap dispute (over USD 100m) involving legal proceedings in England & Shanghai.
Representing a client in a High Court claim for break costs payable under certain loans to European wind farm companies following the pre-payment of those loans.
Representing a client in a High Court claim relating to an alleged agreement to purchase debt on the secondary market.
Representing a client in a dispute before the Hong Kong and English Courts concerning an unfair prejudice claim alleging default and breach of duty by a shareholder/executive.
Representing a large corporate client in a High Court case concerning a completion account dispute following a company acquisition.

International Arbitration

Representing CA Brazil Investment S.A., a Brazilian subsidiary of Paper Excellence, a global leader in pulp, paper and wood products manufacturing in a much-publicised dispute worth over USD 3bn with Brazilian companies owned by prominent Brazilian businessmen. The dispute related to the acquisition of a commodity producer in Brazil. The dispute spanned 6 years, involved four arbitrations, including three ICC arbitrations, and multiple court proceedings in several jurisdictions. We played an instrumental role in securing a global settlement between the parties.
Representing an international mining company as the Respondent in a USD 2bn ICC arbitration dispute against a European energy trading company under a coal supply agreement concerning delivery obligation and broader JV issues relating to the financing of the project.
Representing the main contractor in an approximately EUR 1.2bn LCIA arbitration in relation to the suspension and later termination of a major off-shore gas pipeline construction project.
Representing a Malaysian investor in connection with two large-scale mining projects in Poland in a USD 500m ICC investment treaty arbitration involving allegations of expropriation, breaches of the FET and FPS standards, and a breach of the obligation to encourage and create favourable conditions for foreign investors pursuant to the Malaysia-Poland Bilateral Investment Treaty.
Representing the Respondent in an ICC dispute valued at no less than USD 200m with an international mining company concerning enforcement under debt security agreements.
Representing a group of investors in a large-scale mining project in Eastern Europe in a USD 220m UNCITRAL investment treaty arbitration claim against the host State involving allegations of expropriation and breaches of the FET standard
Representing an international telecoms company in LCIA arbitration proceedings concerning a shareholder dispute (for approximately USD 125m) relating to a national telecoms company within a large African telecoms group.
Representing a LATAM company in several LMAA disputes valued at USD 75m against its JV partner concerning time-charter agreements relating to the provision of services for off-shore oil rigs.
Acting for an international bank in disputes with a large number of ship owners and charterers (over 800 LMAA arbitrations and court proceedings worldwide and almost 200 vessel arrests) arising out of the bankruptcy of a large marine bunker supplier, including an expedited test case in which the client succeeded before the arbitral tribunal, the English High Court, Court of Appeal and Supreme Court.
Representing a group of international gas suppliers in LCIA proceedings regarding an approximately USD166m price dispute under a gas purchase agreement with a CIS state.
Representing a hedge fund founder in LCIA arbitration proceedings concerning an investor dispute in relation to a large hedge fund.
Representing a HNW client in a multi-billion USD LCIA arbitration relating to a Russian prime real estate dispute, involving hearings in both New York and London.
Representing an international media company in a large LCIA commercial arbitration in a dispute relating to a printing contractor agreement.