Michel Deffayet is an engineer graduate from the French National School of Public Works and the French National School of Bridges and Roads. He started his career in the field of underground works with an involvement in many French road tunnel projects.

In 1995, he became the Head of the Environment and Infrastructure Engineering Department of the Centre for Technical Infrastructure Studies in Metz (France) and supervised several motorway project studies.

In 1999, he joined the Departmental Infrastructure Directorate in the Lyon area, where he was in charge of urban planning and transport.

From 2004 to 2022, he was the Director of the CETU (French Centre for Tunnel Studies) with a personal involvement in a wide range of tunnelling activities, covering civil engineering matters, in addition to equipment and operation-related aspects of tunnels. He was notably involved in the production of regulatory texts and guidelines, research and development in the field of underground works, consultancy, assistance for tunnel owners and training actions.

During the same period, he was also the French Government representative within the National Commission for the evaluation of road tunnel safety.

Since 2018, he has been the President of the French Tunnelling and Underground Space Association (AFTES)

On an international level, he has been active in training activities for a long time as Vice Chairman of the ITA Committee on Education and Training (ITA-CET Committee). He is currently President of the ITACET Foundation.