Career in the energy sector
In 1984, Mestrallet started working as a special advisor for Suez.[5] He has been its Chairman and CEO since 2001. He was named Deputy Delegate General for Industrial Affairs in June 1986. In July 1987, he was General Director of the European Court of Human Rights, an affiliate of the Compagnie financière de Suez. In January 1991 he started as the Deputy Director General of the company, but a month later he became the Managing Director and Chairman of the Management Committee of the Société General de Belgique.
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[6] 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.[5][6] 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.[5]
In July 2008, Mestrallet was appointed CEO of GDF Suez (later Engie). Upon merging Gaz de France and Suez to create a new European energy company, he spent about 4 billion euros ($5.6 billion) in a series of targeted acquisitions across the globe by late 2008. He also set a target for the group of investing 10 billion euros a year over the period from 2009 until 2011.[7]
In 2012, GDF Suez's board of directors extended the age limit for the group's chairman and chief executive to 67 from 65, a step that enabled Mestrallet to extend his tenure.[8]
On 3 May 2016, Mestrallet left his position due to statutory age limits[9] and instead became chairman of the board of directors of the group, with Isabelle Kocher appointed as CEO, as planned for months.[10]