In 1988 he joined the environmental movement “France Nature Environnement” and in the following year joined The Greens. From 1992 to 1994 he was the National Secretary of “EcoloJ”, a youth environmental organisation. After completing his studies of fine arts in Strasbourg in 1994, he worked as an illustrator in publishing, for the French-German television channel Arte, and for the Irish channelTnAG. He then became a spokesman for The Greens. In January 2005 he was elected the National Secretary of The Greens with 62% of the vote, coming after long and protracted negotiations. In December 2006 Cécile Duflot succeeded him to the post.
He belonged to the environmentalist wing of the party, named “Pôle Écolo” (the Eco-Pole) ou “Écolo” (Eco). He worked with fellow Green politicians in the European Parliament.
In 2008 he became a member of François Bayrou’s Democratic Movement.
He is a specialist in wild fauna, and an expert on the reintroduction of the lynx into the Vosges forest.