Oyat avocats - Marie-Hélène Tonnellier

Marie-Hélène Tonnelier

Founding Partner · Digital/IP

Oyat avocats - Marie-Hélène Tonnellier

Member of the Paris Bar since 1990, Marie-Hélène co-founded Oyat in 2022.

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!



  • 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



French, English



  • Lecturer at the University Paris XI-Saclay, Master Intellectual Property and Digital Law
  • Lecturer at the HEAD school, Master Digital and Intellectual Property Law
  • Former President of the IFCLA
  • Member of the Board of Directors of AFDIT
  • Member of the International Bar Association (IBA)




Legal 500 EMEA 2024 

  • Marie-Hélène Tonnellier / Leading individual – Tier 1
  • IT and internet – Tier 3

‘Marie-Hélène Tonnellier and her team have a wide range of skills and experience that cover the broad range of TMT issues and the standards of excellence are high whatever the issue. I am therefore able to refer work to them with absolute confidence in their knowledge of their sector particularly with regard to artificial intelligence, data exchange and new developments such as the Data Act and the Data Governance Act, which are raising important new challenges for our clients.’

‘Although the team is small, it is comprehensive in its coverage of the technology sector. The team is experienced and is very much at the forefront of developments in the technology sector.’

‘They are always responsive and provide very clear and practical advice. We have full confidence in them and their abilities, particularly to deal with English-speaking clients. They are also very reasonable in terms of fees.’

‘Marie-Hélène Tonnellier is a well-known name in the technology sector and is always seen at the key technology law conferences, both as participant and speaker. She has incredible breadth of expertise and is always super responsive. She works very hard for clients and is passionate about getting the best outcomes for them. As well as her incredible technical abilities she is also extremely charming and wonderful to work with. I would highly recommend her to my clients and have done so on many occasions over the years.’

‘Highly responsive and display an excellent sense of understanding client needs. They are very easy to deal with and this is achieved by establishing an excellent relationship of trust and confidence. Their fees are reasonable and they provide commercial and pragmatic solutions that are clearly explained and expertly documented.’



Chambers 2024

  • TMT Information Technology



Best Lawyers 2024

  • Advertising Law
  • Information Technology Law
  • Intellectual Property Law



Palmarès of “les meilleurs cabinet d’avocats en France 2024” by le Point

  • New Technologies, IT and Communication Law / 5 stars
  • Literary and artistic property law / 5 stars
  • Intellectual Property Law / 4 stars



Best Lawyers 2024 & 2023

“Lawyer of the Year”



Décideurs Juridiques / Leaders League 2023

/ Innovation, Technology & Telecoms

  • Data protection law / Excellent
  • IT, software & digital projects / Excellent
  • Internet / Excellent

/ Medias & Entertainment

  • Online gaming and betting / Excellent



Who’s Who Legal 2022-2023

  • Data – Data Privacy & Protection 2023, Data Information Technology 2023 / Global Leader
  • Data – Information Technology 2023 / Global Leader
  • France – Data 2023 / National Leader