Chambers 2026
- TMT Information Technology – Marie-Hélène is ranked Band 2
“Marie-Hélène is a very reliable adviser, and the quality of her advice is highly appreciated.”
- The dedicated team is ranked Band 4
Marie-Hélène Tonnellier
Partner · Digital & innovation
A member of the Paris Bar since 1990, Marie-Hélène co-founded the law firm Oyat in 2022. She heads the IT and internet practice within the Digital & Innovation team and co-leads the AI practice alongside Stéphanie Lapeyre-Castellane.
Marie-Hélène began her career in London within a solicitors’ firm prior to joining Moquet Borde & Associés (Paul Hastings) in 1990, then Jeantet in 1995. Then she has been a partner for 22 years at Latournerie Wolfrom Avocats where she created the digital and intellectual property department.
Marie-Hélène is one of the leading lawyers in the digital world. She advises and litigates on all issues related to IT projects, innovations (AI, robots, etc.), e-commerce and personal data. She also intervenes in media law and intellectual property.
Highly skilled in the sectors of distribution, tourism, luxury, new economy, mobility, media or services, she assists her clients in the implementation of strategic projects or in their digital transformation, helps them navigate through the various new rules in these various fields, assists them in often complex and innovative litigations.
Her oyat is between the Garde Guérin and petite Salinette beach: her breton paradise!
EDUCATION
- University of Panthéon-Sorbonne Paris I – Post graduate degree (DEA) in Business Law
- University of Panthéon-Assas Paris II – Post graduate degree (DESS) of Notary Law
- University of Panthéon-Sorbonne Paris I – Master’s Degree Droit des affaires
LANGUAGES
French, English
ACTIVITIES
- Lecturer at the University Paris XI-Saclay, Master Intellectual Property and Digital Law
- Lecturer at the HEAD school, Master Digital & Intellectual Property Law
- Former President of the IFCLA
- Member of the Board of Directors of AFDIT
- Member of the International Bar Association (IBA)
RANKINGS & AWARDS
Chambers 2026
Legal 500 EMEA 2025
- IT and Internet – Tier 3 – Leading Partners
‘ Marie-Hélène Tonnellier is a well-known name in the technology sector. She has incredible breadth of expertise and is always super-responsive.’
‘Marie-Hélène Tonnelier has great expertise and experience.’
‘The Oyat firm, and in particular its founding partner, Marie-Hélène Tonnellier, offers a very operational approach in their consulting activity. The solutions proposed are innovative but pragmatic and adapted to the size of their client and their prospects.’
‘The team is very easy to approach.’
‘Strong and diversified expertise and very good knowledge of several sectors of activity and markets.’
‘Marie-Hélène Tonnelier has a very high level of expertise and experience in the field.’
Décideurs Juridiques / Leaders League 2025 - 2026
/ Innovation, technology & telecoms
- IT, software & digital projects : Leading
- Data Protection Law and Cybersecurity : Excellent
- Digital Platforms Law and Applications : Excellent
Le Point 2025
- New Technologies, IT and Communication Law / 5 stars
Best Lawyers 2026
- Tier 1 Information Technology
- Tier 1 Privacy and Data Security Law
- Tier 1 Technology Law
- Tier 2 Intellectual Property
- Tier 3 Media
Who’s Who Legal 2025
- Data – Data Privacy & Protection 2025, Data Information Technology 2024 / Thought Leaders
- Data – Information Technology 2025 / Thought Leaders
- France – Data 2025 / Thought Leaders
