The siege of Acre of 1799 was an unsuccessful French siege of the Ottoman city of Acre and was the turning point of Napoleon's invasion of Egypt and Syria, along with the Battle of the Nile. It was Napoleon's third tactical defeat in his career, being defeated at the Second Battle of Bassano and the Battle of Caldiero three years previously during the Italian campaign, and his first major strategic defeat, along with the last time he was defeated in battle for 10 years. As a result of the failed siege, Napoleon retreated two months later and withdrew to Egypt.

Acre was a site of significant strategic importance due to its commanding position on the route between Egypt and Syria. Bonaparte wanted to capture it following his invasion of Egypt. He hoped to incite a Syrian rebellion against the Ottomans and threaten British India. After the siege of Jaffa, which was followed by two days and nights of massacre and rape by the French forces,^{[citation needed]} the defenders of the citadel were even more determined to resist the French.

The French attempted to lay siege on 20 March using only their infantry. Napoleon believed the city would capitulate quickly to him. In correspondence with one of his subordinate officers he voiced his conviction that a mere two weeks would be necessary to capture the linchpin of his conquest of the Holy Land before marching on to Jerusalem.

However, the troops of the capable Jezzar Pasha, refusing to surrender, withstood the siege for one and a half months. Haim Farhi, al-Jazzar's Jewish adviser and right-hand man, played a key role in the city's defence, directly supervising the battle against the siege. After Napoleon's earlier capture of Jaffa, rampaging French troops had savagely sacked the captured city, and thousands of Albanian prisoners of war were ordered by Napoleon to be massacred on the sea-shore, prior to the French offensive further northwards. These facts were well known to the townspeople and defending troops (many of them Albanians) in Acre, and the prospect of being massacred is likely to have stiffened their resistance.

A Royal Navy flotilla under Commodore Sidney Smith, commanding Tigre, helped to reinforce the Ottoman defences and supplied the city with additional cannon manned by sailors and marines. Smith used his command of the sea to capture the French siege artillery being sent by a flotilla of gunboats from Egypt and to bombard the coastal road from Jaffa. The captured boats were:

An artillery expert from the fleet, French émigré Antoine de Phélippeaux, then redeployed against Napoleon's forces the artillery pieces which the British had intercepted.

Smith anchored the British ships Tigre and Theseus so their broadsides could assist the Ottoman defence. British gunboats, which were of shallower draft, could come in closer, and together they helped repel repeated French assaults.

On 16 April an Ottoman relief force was fought off at Mount Tabor. By early May, replacement French siege artillery had arrived overland and a breach was forced in the defences. At the culmination of the assault, the besieging forces managed to make a breach in the walls.