Since 2012, William is actively involved in the NGO Friendship. He is the chairman and pro-bono executive director of Friendship France since 2015, and a member of the board of Friendship International. Since 2015 William relaunched Friendship France and developed the activities and programs for access to health, climate change adaptation and education. He has been particularly involved in the Rohingyas crisis.
Alongside his activities within Friendship, William runs BlueRep, a consulting firm specialising in accompanying decision-makers in their purpose-driven approach and strategic project.
He started his career at the Association for the Monetary Union of Europe, a European think tank in charge of the euro changeover. He then spent 10 years in the consulting sector, as a managing partner of a communication group. He has also been a lecturer at Sorbonne University on risk and reputation management.