He was a member of the Saint-Simon Foundation think-tank. Blanc was elected to the National Assembly to represent the third district of Yvelines on 15th December 2002, replacing Anne-Marie Idrac, who had stood down to on nomination to become president of the RATP. He was a member of the UDF, and a supporter of the presidential candidacy of Nicolas Sarkozy in the 2007 presidential election and then member of the new Nouveau Centre.
On March 16, 2008, he failed in the French local elections to become the mayor of Le Chesnay, a wealthy west suburb of Paris. Two days later, he was appointed Secretary of State of Région Capitale ("Great Paris"), a new position in the French Government of François Fillon.