Fort Pitt was a fort built by British forces between 1759 and 1761 during the French and Indian War at the confluence of the Monongahela and Allegheny rivers, where the Ohio River is formed in western Pennsylvania (modern day Pittsburgh). It was near (but not directly on) the site of Fort Duquesne, a French colonial fort built in 1754 as tensions increased between Great Britain and France in both Europe and North America. The French destroyed Fort Duquesne in 1758 when they retreated under British attack.

Virginia colonial protection of this area ultimately led to the development of Pittsburgh and Allegheny County, Pennsylvania by British-American colonists and immigrants.

In April 1754, the French began building Fort Duquesne on the site of the small British Fort Prince George at the beginning of the French and Indian War (AKA Seven Years' War). The Braddock expedition, a 1755 British attempt to take Fort Duquesne, met with defeat at the Battle of the Monongahela at present-day Braddock, Pennsylvania. The French garrison later defeated an attacking British regiment in September 1758 at the Battle of Fort Duquesne. French Colonel de Lignery ordered Fort Duquesne destroyed and abandoned at the approach of General John Forbes' expedition in late November.

A number of factors contributed to this strategic withdrawal. In August 1758 the French Fort Frontenac, at the head of Lake Ontario, was captured by British Gen. Bradstreet, severing the supply lines to French fortifications across the frontier. Fort Duquesne was the southernmost of these. Short on materiel, French commander François-Marie Le Marchand de Lignery was forced to dismiss elements under his command down the Ohio River to their bases in Illinois and Louisiana, and send others overland north to Ft. Presque Isle. Those Native who may have remained at Fort Duquesne were likely eager to return to their winter longhouses before the weather changed. Consequently, the fort was further undermanned, possibly left with as few as 200 regulars.

The late October Treaty of Easton with several Native tribes involved in the war largely dissolved the alliance that had enabled French military dominance in the region. Chiefs of 13 American Indian nations agreed to negotiate peace with the colonial governments of Pennsylvania and New Jersey and to abandon any alliances with the French. The nations were primarily the Six Nations of the Iroquois League, bands of the Lenape (Delaware), and the Shawnee. They agreed to the treaty based on the colonial governments' promising to respect their rights to hunting and territory in the Ohio Country, to prohibit establishing new settlements west of the Appalachian Mountains, and to withdraw British and colonial military troops after the war.

The French commander, anticipating an attack along Braddock's road, had spent some effort fortifying positions there. (Forbes had several times advanced men along that route as a feint.) From prisoners captured during Maj. James Grant’s catastrophic attack on Fort Duquesne, de Lignery was reportedly surprised to learn of a fortified encampment of British troops only 50 miles away at Ligonier, Pennsylvania, with substantial reserves behind. He was also certainly cognizant of the British lightning raid on the Native village of Kittanning (40 miles north on the Allegheny River) two years earlier. Thus, a British attack from the north was a distinct possibility. Forbes had indeed contemplated an attack further north on Fort Machault (later, Ft. Venango; modern-day Franklin, PA.)

Finding himself in an under-manned, flood-prone fort in a weak defensive position, vulnerable to attack from three directions, and running low on provisions, de Lignery retreated north. He destroyed the stores and many of the structures as 1500 advance British troops under the command of Forbes drew within 10 miles. The French never returned to the region.

After constructing the temporary Mercer's Fort, the British built a new fort and named it Fort Pitt, after William Pitt the Elder. The fort was built from 1759 to 1761 during the French and Indian War (Seven Years' War), next to the site of former Fort Duquesne. It was built in the popular pentagram shape, with bastions at the star points, by Captain Harry Gordon, a British Engineer in the 60th Royal American Regiment.