A graduate of École Polytechnique (X92 class) and a doctor in cryptology, Guillaume has worked for the French Prime Minister and Ministry of Defense, where he specialized in cybersecurity and cyberdefence. From 2014 to 2022 he has been director deneral of ANSSI, the French National Cyber Security Agency. Since January 2023, he has been Deputy Managing Director of Docaposte (La Poste Groupe), a leader in trusted digital technologies, in charge of technological assets around artificial intelligence, cyber, IT and cloud computing. Since July 2025 he is also co-chairman of the French AI and Digital National Council.