Eärnur was the son of Eärnil II and he was the thirty-third and last King of the South-kingdom until the restoration of Elessar Telcontar in TA 3019.

In the autumn of TA 1973, during the reign of his father Eärnil, messages came to Gondor from Arvedui, King of Arthedain, asking for help in the war with the Witch-king of Angmar. Eärnil sent his son north with a great fleet, but they arrived too late at the Grey Havens, for Arthedain had already been defeated and Arvedui had perished.

Then Círdan gathered more forces from Lindon and Arnor, and together with Eärnur’s host marched north to meet the Witch-king. The confrontation took place on the plain between Nenuial and the North Downs and the armies of Men and Elves succeeded in utterly defeating the forces of Angmar. In the end the Witch-king himself appeared on the battlefield and challenged Eärnur, who would have withstood him, but his horse fled in terror before he could control it. Then the Witch-king passed into shadows and returned to Mordor, but the victorious host saw nothing of this, and when Eärnur came back and intended to pursue the Witch-king, being angry of the humiliation suffered, Glorfindel advised him not to do so, foretelling that the Witch-king’s doom was still far away and could not be achieved by any man.

After Eärnur’s succession to the throne of Gondor in TA 2043, he was again challenged by the Witch-king to single combat, but Mardil the Steward managed to restrain the King from accepting the challenge. It was during Eärnur’s reign that the capital of the South-kingdom, Minas Anor, was renamed Minas Tirith, the Tower of Guard, for its chief concern was from that time on to guard Gondor of the evil dwelling in Minas Morgul.

In TA 2050, the Witch-king renewed his challenge to Eärnur, and this time Mardil couldn’t restrain the King anymore. Eärnur took a small escort of knights and rode to Minas Morgul to meet the Witch-king. Nothing is known of the fate that befell them, though it was later believed in Gondor that the Witch-king had deceived the King and put him to death through long torments.

Eärnur ruled Gondor for 7 years (TA 2043 - 2050) and after his disappearance there was no valid claim to the throne, all fearing the memory of the dreadful Kin-strife. So it was that after Eärnur the South-kingdom was ruled by the Stewards, the first being Mardil Voronwë.