Europe Ecology – The Greens
First elected to the National Assembly in the 2007 legislative election, he was reelected in 2012. In 2012, he was elected to the co-presidency of the newly-founded Ecologist group, alongside Barbara Pompili. In 2015, he broke with Europe Ecology – The Greens to form a new party with Jean-Vincent Placé, the Ecologist Party, which supported the administration of President François Hollande. He was succeeded as group co-president by Cécile Duflot before regaining the office following the Pompili's appointment as Secretary of State for Biodiversity.