Born in Aix-en-Provence, he was the son of Joseph-Sextius Siméon (1717–1788), a professor of Law and royal secretary for the parlement of Provence.
Joseph Jérôme Siméon followed his father's profession, but he was a pursued under the Reign of Terror for his share in the Girondist movement in 1793, and only returned to France after the Thermidorian Reaction.
In the Tribunate, Siméon had an important share in the preparation of the Napoleonic Code, being rewarded by a seat in the Conseil d'État of the French Consulate.
In 1820, he was under-secretary of state for Justice, and in the next year Minister of the Interior until the fall of the Armand-Emmanuel Richelieu ministry (12 December 1821).
[1] A baron of the Empire, created count by the Restoration, he was admitted to the Academy of Political and Moral Sciences in 1832, and in 1837 he became president of the Cour des Comptes.