Jean Sébastien Mariez

Attorney at Law - Partner

For the past 15 years, Jean-Sébastien has helped players in the digital economy by protecting their innovation (software, databases, artificial intelligence, e-commerce platforms), securing their business activities (personal data, cybercrime, e-reputation) and providing representation in litigation before civil, commercial and criminal courts (piracy, unfair competition, Internet) and supervisory authorities. His practice focuses on ICT service activities, Media, Gaming, Luxury and Consumer goods.

Jean-Sébastien also advises on public and regulatory affairs in order to facilitate early awareness and integration of significant regulatory changes impacting the activity of his clients. In this capacity, he has been active recently in the context of the adoption of the French “Hate speech Act”, “Fake news Act” as well as the transposition of European Directives and Regulations.

Before founding Momentum Avocats, Jean-Sébastien worked as a partner in the law firm De Gaulle Fleurance & Associés, which he joined after practicing in-house at Microsoft where he served as Head of the Cybersecurity and Anti-Piracy division of the French Legal & Corporate Affairs Department.

Jean-Sébastien was involved for ten years with the association Avocats Sans Frontières, where he actively contributed to the raising of European funds, the management of mass litigation programs relating to the violation of human rights and the release of convicted women at the end of proceedings initiated before the ECOWAS Court.

Jean-Sébastien holds a Master of Laws (LL.M.) in European Business Law from the University of Nancy II (2001) and a DESS post-graduate degree in Politics and International Relations from Paris XI University (2002). He has been a member of the Paris Bar since 2005.

Jean-Sébastien rankings are the following: Legal 500 (Information technology, computing and internet ; Data protection) – Best Lawyers (Information Technology Law ; Litigation ; Technology Law)


French, English

Rest of the team

Julien Canlorbe

Attorney at Law - Partner

Julie Carel

Attorney at Law - Partner

Laure Meysonnet

Attorney at Law - Associate

Laura Godfrin


Valentine Giraudat

Attorney at law - Associate

Philomène Dubecq

Attorney at law - Associate

Jeanne Roussel


Lucie Bureau

Attorney-at-Law - Associate

Inès Lalet

Trainee lawyer

Raphaël Gentilleau

Trainee Lawyer


Intellectual Property

Trademarks, brand and design protection

Licensing and transactions

IP litigation


Designations of origin

Information Technology

Online content disputes

IT litigation

IT agreements

Artifical intelligence

Blockchain and Web 3

Access and use of public data

IT Regulatory

Media, Entertainment & Sports


News - Book publishers

E-reputation – Influencers

Defamation - Image Rights

Sports - Gaming

Commercial and E-commerce

Commercial litigation


Commercial agreements and Distribution

Consumer Law

Data Privacy and cybersecurity

Personal Data compliance

Personal Data litigation


Privacy Regulatory