It was here that Elendil landed after the destruction of Númenor and went out to find Gondor and Arnor. It was rebuilt during the tenth century of the Third Age by Eärnil I, and became the main base of power for the mighty Ship Kings of Gondor in their struggles with their rivals, the Black Númenórians of the city-port of Umbar, far to the south in the land of Harad.
During the Gondor's civil war in 1447, Pelargir was seized by the rebels, but was regained after a year-long siege. Although suffering most of the same ills that afflicted all of Gondor, and often attacked by Haradrim, Easterlings and the Corsairs of Umbar, Pelargir survived as the chief port of Gondor until the War of the Ring. Only then were the black ships of the Corsairs able to overcome the defences of Pelargir, but even so their dominion did not last long.
The Dúnedain chieftain Aragorn brought the phantom army of the Dead Men of Dunharrow and routed the Corsairs, who fled in terror and Aragorn seized the whole of their fleet.

With these captured ships, Aragorn was able to bring the Men of Pelargir up the River Anduin in that last defence of Gondor on Pelennor Fields and turn the tide of battle.
Through the Fourth Age, Pelargir once more grew wealthy and powerful as the chief port of the Reunited Kingdom.