Finduilas lived in Nargothrond with her father Orodreth under the rule of Finrod Felagund. She was betrothed to Gwindor, who named her Faelivrin, which meant 'Gleam of the Sun in the pools of Ivrin'. She was very beautiful, a high princess of the Noldor and niece of Galadriel.
Her betrothed was captured in 472 of the First Age during the Battle of Unnumbered Tears by Morgoth, but he returned in 490 with a companion who called himself Agarwaen son of Umarth (the Bloodstained, son of the Cursed). Unknown to Finduilas this was actually Túrin son of Húrin.
Despite her old feelings for Gwindor, Finduilas fell in love with Túrin, but Túrin refused her in respect for his friend. Gwindor realized this, and revealed Túrin's name to Finduilas, and tried to persuade Túrin to submit to his feelings for Finduilas, realizing that Finduilas stood between Túrin and the curse of Morgoth.
At the sack of Nargothrond by an army of orcs under the dragon Glaurung, Gwindor was slain and died in the arms of Túrin, whom he told to seek out Finduilas, saying that Finduilas lay between him and his doom. However, when Túrin arrived at the ruins of Nargothrond, he was bewitched by the dragon, and he could not respond to Finduilas' cries as she was dragged past him by the orcs of Morgoth as a slave for Angband.
Due to Glaurung's deceit and manipulation, Túrin failed to follow the trail of Finduilas and instead went to Dor-lómin in search of his lost mother and sister. By the time he finally saw through the dragon's lies and went after his beloved, it was too late. When the Orcs were waylaid by the Haladin of Brethil at the Crossings of Taeglin the orcs killed all of their captives, impaling Finduilas with a spear against a tree. With her dying breath, Finduilas begged the Men of Brethil to tell Túrin where she had fallen.
Later, after partially recovering from his grief, Túrin sought asylum among the Haladin, leading a small party in guerilla attacks against the orcs as they passed through near the mound of his beloved. As a result, the place was soon feared by the orcs and minions of Morgoth. When Nienor arrived in Brethil and was found naked upon the Mound of Finduilas, Túrin, not knowing her to be his sister, declared that the Valar had smiled upon him. They soon married, oblivious to their kinship.
When Glaurung personally attacked Brethil with fire, Túrin was shocked to see the dragon avoid the Mound of Finduilas, although it meant travelling far out of his way. Noting that the dragon's fear of the Mound had bought precious time and allowed him to arrange an ambush, Túrin declared that Gwindor had spoken truth and that Finduilas still stood between him and his doom.