Portalis was born at Le Beausset, currently in the Var département of Provence, France to a bourgeois family, and was educated by the Oratorians at their schools in Toulon and Marseille, and then went to the University of Aix.

As a student, he published his first two works, Observations sur Émile (on Jean-Jacques Rousseau's Emile: Or, On Education) in 1763 and Des Préjugés in 1764.

[2] In 1765 he became a lawyer at the parlement of Aix-en-Provence, and soon obtained so great a reputation that he was instructed by Étienne François de Choiseul in 1770 to draw up the decree authorizing the marriage of Protestants.

[2] In November 1793, after the First French Republic had been proclaimed, he came to Paris and was thrown into prison for being the brother-in-law of Joseph Jérôme Siméon, the leader of the Federalists in Provence.

In 1803 he became a member of the Académie française, in 1804 Minister of Public Worship, and in 1805 a Chevalier Grand-Croix de la Légion d'honneur.