In 1828 Cormenin entered the Chamber of Deputies as member for Orléans, took his seat in the Left Center, and began a vigorous opposition to the government of Charles X. As he was not gifted with the qualifications of the orator, he seldom appeared at the tribune; but in the various committees he defended all forms of popular liberties, and at the same time delivered, in a series of powerful pamphlets, under the pseudonym of "Timon", the most formidable blows against tyranny and all political and administrative abuses. After the revolution of July 1830, Cormenin was one of the 221 who signed the protest against the elevation of the Orléans dynasty to the throne; and he resigned both his office in the council of state and his seat in the chamber. He was, however, soon re-elected deputy, and now voted with the extreme Left.