Soult's intrigues while occupying Portugal earned him the nickname, "King Nicolas", and while he was Napoleon's military governor of Andalusia, Soult looted 1.5 million francs worth of art. One historian called him "a plunderer in the world class."
Soult was born at Saint-Amans-la-Bastide (now called Saint-Amans-Soult, near Castres, in the Tarn departement) and named after John of God. He was the son of a country notary named Jean Soult (1726–1779) by his marriage to Brigitte de Grenier. His paternal grandparents were Jean Soult (1698–1772) and Jeanne de Calvet, while his maternal grandparents were Pierre François de Grenier de Lapierre and Marie de Robert. His younger brother Pierre also became a French general.
Well-educated, Soult originally intended to become a lawyer, but his father's death when he was still a boy made it necessary for him to seek employment, and in 1785 he enlisted as a private in the French infantry.
Soult's superior education ensured his promotion to the rank of sergeant after six years' service, and in July 1791 he became instructor to the first battalion of volunteers of the Bas-Rhin. He was serving in this battalion in 1792. By 1794, he was adjutant-general (with the rank of chef de brigade). After the Battle of Fleurus of 1794, in which he distinguished himself for coolness, he was promoted to brigadier general by the representatives on mission.
For the next five years Soult was employed in Germany under Jourdan, Moreau, Kléber and Lefebvre, and in 1799 he was promoted general of division and ordered to proceed to Switzerland. It was at this time that he laid the foundations of his military fame; he particularly distinguished himself in Masséna's great Swiss campaign, and especially at the Second Battle of Zurich. He accompanied Masséna to Genoa, and acted as his principal lieutenant throughout the protracted siege of that city, during which he operated with a separate force outside the city walls. He was wounded and taken prisoner at Monte Cretto on 13 April 1800.