Arnault was born in Paris. His first play, Marius à Minturne (1791), immediately established his reputation. A year later he followed with a second republican tragedy, Lucrèce. Arnault left France during the Reign of Terror, but on his return, he was arrested by the revolutionary authorities. He was freed through the intervention of Fabre d'Églantine and others. He was commissioned by Napoleon Bonaparte in 1797 with the organization of the Ionian Islands, and was nominated to the Institute and made secretary general of the university. Arnault was faithful to his patron through his misfortunes, and after the Hundred Days remained in exile until 1819. Arnault died at Goderville. 
Other plays of Arnault's are: Blanche et Moncassin, ou les Vénitiens (1798); and Germanicus (1816), the performance of which was the occasion of a disturbance in the parterre which threatened serious political complications. His tragedies are now less well known than his Fables (1813, 1815 and 1826), which are written in graceful verse. Arnault collaborated a Vie politique et militaire de Napoléon 1er (1822), and wrote some very interesting Souvenirs d'un sexagénaire (4 vols, 1833), which contain much out-of-the-way information about the history of the years previous to 1804. Arnault's Œuvres complètes (4 vols.) were published at the Hague and Paris in 1818-9, and again (8 vols.) at Paris in 1824.
Arnault's eldest son, Emilien Lucien (1787–1863), wrote several tragedies, the leading rôles in which were interpreted by Talma.