Details of the original forging of Narsil are difficult to determine. It was made by Telchar of Nogrod, who also made the Dragon-helm of Dor-lómin. Helpfully, a passage in Unfinished Tales tells us that the Dragon-helm was originally made for Azaghâl of Belegost, who died in the Nirnaeth Arnoediad in I 471; in order to make the helm specifically for Azaghâl, Telchar must have been working at about this time. Though we can't be certain exactly when Narsil was made, then, we can fairly safely place its forging in Telchar's workshop in Nogrod, probably during the fourth or fifth centuries of the Years of the Sun.

Narsil was broken in the War of the Last Alliance, with the fall of its wielder Elendil. Its burning light was lost, but Elendil's son Isildur used its broken shards to cut the Ruling Ring from Sauron's finger. The shards were eventually brought to Imladris, and they became an heirloom of the House of Isildur. During the War of the Ring, the sword was reforged, its light was rekindled, and it was borne by Elendil's distant descendant Aragorn, who renamed it Andúril.

The origins of Narsil's name are complex, and contain an element of symbolism. Tolkien himself described the name's derivation in his Letters:

So, an alternative and less literal translation of Narsil would be 'Sun-and-Moon', and indeed we see that formulation in the name of the tale Narsilion, translated as the 'Song of the Sun and Moon'.