His force was out-maneuvered, surrounded, and largely destroyed by the French and their native allies led by François-Marie Le Marchand de Lignery.

After repulsing this advance party, the French, deserted by some of their native allies and vastly outnumbered by the approaching Forbes, blew up their magazines and burnt Fort Duquesne.

In November the French withdrew from the Ohio Valley and British colonists erected Fort Pitt on the site.

On September 11, 1758, Grant led over 800 men to scout the environs of Fort Duquesne ahead of Forbes' main column.

[6] In the one-sided battle in the woods, the British and American force suffered 342 casualties, of whom 232 were from the 77th Regiment, including Grant, who was taken prisoner.

They then flew to arms, and the Indians ran up under cover of the banks of Allegheny and Monongahela, for some distance, and then sallied out from the banks of the rivers, and took possession of the hill above Grant; and as he was on the point of it in sight of the fort, they immediately surrounded him, and as he had his Highlanders in ranks, and in very close order, and the Indians scattered, and concealed behind trees, they defeated him with the loss only of a few warriors; most of the Highlanders were killed or taken prisoners.

The Indians had decapitated many of the dead Highlanders and impaled their heads on the sharp stakes on top of the fort walls, with their kilts displayed below.