Beren was the last survivor of a group of Men led by his father Barahir that had still resisted Morgoth, the Dark Enemy, after the Battle of Sudden Flame, in which Morgoth had conquered much of northern Middle-earth. After the defeat of his companions he fled from peril into the elvish realm Doriath. There he met Lúthien, the only daughter of King Thingol and Melian the Maia, as she was dancing and singing in a glade. Seeing the beautiful Elf, Beren fell in love with her, for she was the fairest of all Elves and Men. She later fell in love with him as well, when he, moved by her beauty and enchanting voice, gave her the nickname "Nightingale." As Thingol disliked Beren and regarded him as being unworthy of his daughter, he set a seemingly impossible task on Beren that he had to achieve before he could marry Lúthien. Thingol asked Beren to bring him one of the Silmarils, the three hallowed jewels made by Fëanor, which Morgoth had stolen from the Elves.
Beren left Doriath and set out on his quest to Angband, the enemy’s fortress. Although Thingol tried to prevent it, Lúthien later followed him. On his journey to the enemy’s land Beren reached Nargothrond, an Elvish stronghold, and was joined by ten warriors under the lead of King Finrod, who had sworn an oath of friendship to Beren's father. Although Fëanor’s sons, Celegorm and Curufin, warned them not to take the Silmaril that they considered their own, the company was determined to accompany Beren. On their way to Angband they were seized by the servants of Sauron, despite the best efforts of Finrod to maintain their guise as Orcs, and imprisoned in Tol-in-Gaurhoth. One by one they were killed by a werewolf until only Beren and Finrod remained. When the wolf went for Beren, Finrod broke his chains and wrestled with it such fierceness that they both died.
When she was following Beren, Lúthien was captured and brought to Nargothrond by Celegorm and Curufin. Aided by Huan, Celegorm’s hound (which according to prophecy could only be defeated by the greatest werewolf ever), she was able to flee. With his aid she came to Sauron’s fortress where Huan defeated the werewolves of the Enemy, Draugluin, and Sauron himself in wolf-form. Then they freed the prisoners, among them Beren.
Beren wanted to try his task once more alone, but Lúthien insisted on coming with him. Through magic they took the shapes of the bat Thuringwethil and the wolf Draugluin that Huan had killed. Thereby they were able to enter the enemy’s land and at last came to Angband and before Morgoth’s throne. There Lúthien sang a magical song which made the Dark Lord fall asleep; then Beren cut a Silmaril from Morgoth’s crown. As he tried to cut out the others, his knife broke and a shard glanced off Morgoth's face, awakening him. As they attempted to leave, the gate was barred by Carcharoth, a giant werewolf, who was bred as an opponent to Huan. He bit off and swallowed Beren’s hand, in which Beren was holding the Silmaril. Carcharoth was burned by the pure light of the Silmaril and ran off madly.
Beren and Lúthien returned to Doriath, where they told of their deeds and thereby softened Thingol’s heart. He accepted the marriage of his daughter and the mortal Man, although Beren’s task had not been fulfilled. Beren and Huan participated in the hunt for Carcharoth, who in his madness had come into Doriath and caused much destruction there. Both of them were killed by the wolf, but Carcharoth was also slain. Before he died, Beren handed the Silmaril, which was recovered from Carcharoth's belly, to Thingol.
Grieving for Beren, Lúthien also died, and came to the halls of Mandos. There she sang of her ill fate, that she would never again see Beren, who as a mortal Man had passed out of the world. Thereby Mandos was moved to pity. He restored Beren and Lúthien to life and granted mortality to the Elf. Lúthien left her home and her parents and went to Ossiriand with Beren. There they dwelt for the rest of their lives, and both eventually died the death of mortal Men.