The siege of Toulon (29 August – 19 December 1793) was a military engagement that took place during the Federalist revolts and the War of the First Coalition, part of the French Revolutionary Wars. It was undertaken by forces of the French Republic against Royalist rebels supported by Anglo-Spanish forces in the southern French city of Toulon. It was during this siege that young Napoleon Bonaparte first won fame and promotion when his plan, involving the capture of fortifications above the harbour, was credited with forcing the city to capitulate and the Anglo-Spanish fleet to withdraw. The siege marked the first involvement of the British Royal Navy with the French Revolution.

After the arrest of the Girondist deputies on the 2 June 1793, there followed a series of insurrections within the French cities of Lyon, Avignon, Nîmes, and Marseille known as Federalist revolts. In Toulon, the federalists evicted the local chapter of the Jacobin Club, but were soon supplanted by the more numerous royalists. Upon the announcement of the recapture of Marseille and of the reprisals which had taken place there at the hands of the revolutionaries, the royalist forces, directed by the Baron Xavier Lebret d'Imbert, requested support from the Anglo-Spanish fleet. On 28 August, the British and Spanish commanders of the fleet, Admiral Sir Samuel Hood (Royal Navy) and Admiral Juan de Lángara (Spanish Navy), responded with 13,000 troops of British, Spanish, Neapolitan and Sardinian origin. Baron d'Imbert delivered the port of Toulon to the British navy.

Toulon hoisted the royal flag, the fleur de lys, and d'Imbert declared the eight-year-old Louis XVII King of France on the first of October. This result produced a potentially mortal situation for the French Republic, as the city had a key naval arsenal and was the base for 26 ships of the line (about one-third of the total available to the French Navy). Without this port, the French could not hope to challenge the Allies, and specifically the British, for control of the seas. In addition, Toulon's loss would send a dangerous signal to others preparing to revolt against the Republic. Although France had a large army due to its levée en masse, the Republic could not easily rebuild its navy, which had been the third largest in Europe, if the Allies and Royalists destroyed or captured much of it. Both the strategic importance of the naval base and the prestige of the Revolution demanded that the French recapture Toulon.

I have no words to describe Buonaparte's merit: much technical skill, an equal degree of intelligence, and too much gallantry ...

— General Jacques François Dugommier, at the siege of Toulon, in a letter to Minister of War Jean Bouchotte

The troops of the army said to be of the "Carmagnoles", under the command of General Jean François Carteaux, arrived at Toulon on 8 September, after those troops had recovered Avignon and Marseille, and then Ollioules. They joined up with the 6,000 men of the Alpine Maritime Army, commanded by General Jean François Cornu de La Poype, who had just taken La Valette-du-Var, and sought to take the forts of Mont Faron, which dominated the city to the East. They were reinforced by 3,000 sailors under the orders of Admiral Jean René César de Saint-Julien de Chabon [fr], who refused to serve the British with his chief, Jean-Honoré de Trogoff de Kerlessy. A further 5,000 soldiers under General La Poype were attached to the army to retake Toulon from the Army of Italy.

The Chief of Artillery, Elzéar Auguste Cousin de Dommartin, having been wounded at Ollioules, had the young captain Napoleon Bonaparte imposed upon him by the special representatives of the National Convention and Bonaparte's friends—Augustin Robespierre and Antoine Christophe Saliceti. Bonaparte had been in the area escorting a convoy of powder wagons en route to Nice and had stopped in to pay his respects to his fellow Corsican, Saliceti. Bonaparte had been present in the army since the Avignon insurrection (July, 1793), and was imposed on Dommartin in this way despite the antipathy between the two men.

Despite the mutual dislike, Bonaparte was able to muster an artillery force that was sufficient for a siege of Toulon and the fortresses that were quickly built by the British in its immediate environs. He was able to requisition equipment and cannon from the surrounding area. Guns were taken from Marseille, Avignon and the Army of Italy. The local populace, which was eager to prove its loyalty to the republic which it had recently rebelled against, was blackmailed into supplying the besieging force with animals and supplies. His activity resulted in the acquisition of 100 guns for the force. With the help of his friends, the deputies Saliceti and Augustin Robespierre, who held power of life and death, he was able to compel retired artillery officers from the area to re-enlist. The problem of manning the guns was not remedied by this solution alone, and under Bonaparte's intensive training he instructed much of the infantry in the practice of employing, deploying and firing the artillery that his efforts had recently acquired. However, in spite of this effort, Bonaparte was not as confident about this operation as was later his custom. The officers serving with him in the siege were incompetent, and he was becoming concerned about the needless delays due to these officers' mistakes. He was so concerned that he wrote a letter of appeal to the Committee of Public Safety requesting assistance. To deal with his superiors who were wanting in skill, he proposed the appointment of a general for command of the artillery, succeeding himself, so that "... [they could] command respect and deal with a crowd of fools on the staff with whom one has constantly to argue and lay down the law in order to overcome their prejudices and make them take steps which theory and practice alike have shown to be axiomatic to any trained officer of this corps".