In 1995 Mestrallet took a position as the head of Suez and from then he worked for Suez while focusing on three businesses: energy, water, and waste He fostered the reconciliation between Suez and the Lyonnaise des Eaux. The Suez-Lyonnaise des Eaux was started in 1997, at which time Mestrallet became the chairman of its executive board while Jérôme Monod, chairman of Lyonnaise, became the Chairman of the Supervisory Board. However, the group soon went back to its original name, Suez and in 2003 its leaders made a proposition to shareholders to change the association of the company by becoming an LP with a board of directors and Gerard Mestrallet as the CEO.