Descended from a noble family of Provence, he was born at Fox-Amphoux. At the age of sixteen he entered the regiment of Languedoc as "gentleman cadet", but embarked for India in 1776. After an adventurous voyage he reached Pondicherry and shared in the defence of that city, which ended in its capitulation to the British on 18 October 1778. On the release of the garrison, Barras returned to France. After taking part in a second expedition to the East Indies in 1782 - 1783, he left the army and occupied the following years with the frivolities congenial to his class and to his nature.
At the outbreak of the French Revolution in 1789, he espoused the democratic cause, and became one of the administrators of the département of the Var. In June 1792 he took his seat in the high national court at Orleans; and later in that year, on the outbreak of war with the kingdom of Sardinia, he became commissioner to the French army of Italy, and entered the National Convention (the third of the national assemblies of France) as a deputy for the département of the Var. In January 1793 he voted with the majority for the death of Louis XVI. Much of his time, however, was spent in missions to the districts of the south-east of France; and in this way he made the acquaintance of Bonaparte at the siege of Toulon. As an example of the incorrectness of the Barras Memoirs we may note that the writer assigned 30,000 men to the royalist defending force, whereas it had fewer than 12,000; he also sought to minimize the share taken by Bonaparte in the capture of that city.
In 1794 Barras sided with the men who sought to overthrow the Robespierre faction, and their success in the coup d'état of Thermidor (27 July 1794) brought him almost to the front rank. In the next year, when the Convention felt threatened by the malcontent National Guards of Paris, it appointed Barras to command the troops engaged in its defence. His nomination of Bonaparte led to the adoption of vigorous measures, which ensured the dispersion of the royalists and malcontents in the streets near the Tuileries, 13 Vendémiaire (5 October 1795). Thereupon Barras became one of the five Directorss who controlled the executive of the French republic.
Owing to his intimate relations with Josephine de Beauharnais, Barras helped to facilitate a marriage between her and Bonaparte; and many have averred, though on defective evidence, that Barras procured the appointment of Bonaparte to the command of the army of Italy early in the year 1796. The achievements of Bonaparte gave to the Directory a stability which it would not otherwise have enjoyed; and when in the summer of 1797 the royalist and constitutional opposition again gathered strength, Bonaparte sent General Augereau, a headstrong Jacobin, forcibly to repress that movement by what was known as the coup d'état of 18 Fructidor (4 September 1797). Barras and the violent Jacobins now carried matters with so high a hand as to render the government of the Directory odious; and Bonaparte had no difficulty in overthrowing it by the coup d'état of 18 - 19 Brumaire (9 - 10 November 1799).
Barras saw the need of a change and was to some extent (how far will perhaps never be known) an accomplice in Bonaparte's designs, though he did not suspect the power and ambition of their contriver. He was left on one side by the three Consuls who took the place of the five Directors and found his political career at an end. He had amassed a large fortune and spent his later years in voluptuous ease.
Among the men of the Revolution few did more than Barras to degrade that movement. His immorality in both public and private life was notorious and contributed in no small degree to the downfall of the Directory, and with it of the first French Republic.
Despite his profession of royalism in and after 1815, he remained more-or-less suspect to the Bourbons. On his death it was with some difficulty that the notes for his memoirs were saved from seizure.
Paul Barras died on January 29, 1829 and was interred in the Pere Lachaise Cemetery, Paris, France.