A lawyer and provincial administrator at Aix-en-Provence, Portalis went to Paris in 1793, after the First Republic had been proclaimed following the Revolution. In 1795 he was elected to the legislative body called the Council of Elders (Conseil des Anciens), and later he became its president. In 1800 Napoleon Bonaparte (Napoleon I), then first consul, made Portalis a councillor of state and a member of the four-man commission charged with drawing up the Civil Code, which was promulgated March 21, 1804. Considered the most hardworking of the four, Portalis wrote several of the most important articles of the code, notably those on marriage and succession to property. His effort was to permeate the code with the ideals of Roman law.

In 1801 Portalis was placed in charge of cultes, or state-controlled public worship. In that office, he drew up much of the concordat of July 15, 1801, between Napoleon I and Pope Pius VII.