After leading the defences of Osgiliath against Sauron in June III 3018, he set out to Rivendell to find answer to a riddling dream he and his brother were seeing. He participated in the Council of Elrond, where he is described as a tall man with a fair and noble face, dark-haired and grey-eyed, proud and stern of glance. He was cloaked and booted as if for a journey on horseback; and indeed though his garments were rich, and his cloak was lined with fur, they were stained with long travel. He had a collar of silver in which a single white stone was set; his locks were shorn about his shoulders. On a baldric he wore a great horn tipped with silver that now was laid upon his knees.

He set out from Rivendell with Company of the Ring. During the journey, at least since Lórien, the Ring was tempting him, thinking that he could use it for Gondor's sake. On Amon Hen he attempted to kill Frodo and get the Ring, but he immediately repented. This however drove Frodo to abandon the Fellowship and continue alone his Quest. If it weren't for Boromir, Frodo would have been captured by the Orcs who attacked Amon Hen later that day. After killing many Orcs, Boromir died by arrows protecting Merry and Pippin, who were afterwards captured.

He was found near death by Aragorn and then with Gimli and Legolas, he gave him a proper funeral and set his body afloat down Anduin. The boat was seen by Faramir on Anduin and his body was buried in the Hallows.