The son of an army contractor, Vergniaud attended college in Paris and in 1781 became an advocate in the Parlement (high court of justice) of Bordeaux. Although he was a capable lawyer, he was so indolent that he refused to take cases unless he was in need of money.

Vergniaud greeted the outbreak of the Revolution with enthusiasm. In 1790 he attracted widespread attention by pleading the case of a soldier who had been involved in a riot against a landlord. Elected to the administration of the Gironde département (1790), he looked on with approval as the revolutionary National Assembly in Paris abolished France's feudal institutions and restricted the hitherto absolute powers of King Louis XVI. Vergniaud took a seat with the other Girondin deputies in the Legislative Assembly, which succeeded the National Assembly on Oct. 1, 1791, and he spoke with eloquence in favour of war with Austria. After war was declared (April 20, 1792), he exposed Louis XVI's counterrevolutionary intrigues and suggested (July 3) that the King should be deposed. Nevertheless, unlike their Jacobin rivals, Vergniaud and the other Girondins were unwilling to form ties with the disenfranchised lower classes. Faced with the threat of popular insurrection in Paris, Vergniaud attempted secretly to come to terms with the King in late July. The populace of Paris rose against Louis on August 10, and Vergniaud, as president of the Assembly, was forced to propose the suspension of the King and the summoning of a National Convention.

In the Convention, which met on Sept. 20, 1792, Vergniaud avoided attacking the Montagnards (Montagnard) (as the Jacobin deputies were called) until they revealed (Jan. 3, 1793) his previous negotiations with the King. During the trial of Louis XVI, Vergniaud at first sought to save the monarch's life, but he finally joined the majority in voting (January 1793) for the death sentence. On June 2, 1793, Parisian insurgents, in alliance with the Montagnards, forced the convention to place Vergniaud and 28 other Girondin leaders under house arrest. Vergniaud continued to defy his opponents but made no attempt to escape from Paris. Imprisoned on July 26, he was condemned by the Revolutionary Tribunal on October 30 and guillotined the following day.