
- Profile
Testimonials
Collated independently by Legal 500 research team.
‘ 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.’
‘Very good business expertise and very good communication.'
‘We frequently work with the Oyat team on IT, e-commerce, data protection matters and more recently on AI matters. I particularly value their technical legal skills which are delivered through the lens of being highly commercial and pragmatic.'
Key clients
- SOPRA STERIA
- NOUVELLE AQUITAINE MOBILITES
- NEOCASE
- MAINCARE
- IMKI
- KEYSQUARE
- EDREAMS ODIGEO
- THE METRICS FACTORY
- OMNES
- SNCF CONNECT
Work highlights
- Assisted Eurovision on various matters in IT, data and telecommunications in particular in the negotiation of an IT agreement with an IT company from Israel, providing new features and functionalities implemented in the Eurovision’s IT system in order to facilitate the broadcast of its programmes.
- Assisting IMKI, an IT company which creates AI specialised for fashion designers, helping them to conceive and create fashion collections.
- Assisting Sopra Steria in several IT projects.
Lawyers
Leading partners
The strongest partners in their field, leading on market-leading deals and endorsed by peers and clients alike.

Leading associates
Leading associates with regular involvement in their team's key work, and recognition from peers or clients as being ones to watch.
Charlotte Barraco-David
Practice head
Marie-Helene Tonnellier
Other key lawyers
Charlotte Barraco-David