Lenwë was an Elf of the Telerin clan, who set out with the Great Journey of the Elves into the West. When his people found their path blocked by the Misty Mountains, he resolved to leave the Journey and instead led his followers south down the Vales of Anduin, and they became known as the Nandor. After many years, Lenwë's son Denethor set out westward once again, and led some part of the Nandor across the Misty Mountains and the Blue, settling at last in the Land of Seven Rivers beneath the Ered Luin; the land called Ossiriand.
Denethor and his followers did not have peace for long. Soon after his return to Middle-earth, before the Noldor had followed him, Morgoth loosed armies of orcs on King Thingol and his allies, Círdan in the west and Denethor in the east. Denethor's Nandor were ill-equipped for warfare, and suffered great hardship in that battle. Denethor himself was slain on Amon Ereb, though the Elves beat back the orcs at last. After that time many of Denethor's people left Ossiriand for the guarded forests of Doriath. Those few that remained took up a secretive existence, camouflaging themselves in green. From that time, they were known as the Green-elves, or Laiquendi in the Elvish tongue.
The hidden people of the Green-elves played little part in history after the First Battle of the Wars of Beleriand. Most significantly, they lent their aid to Beren and Dior (who dwelt on Tol Galen in the far south of their land). After the loss of their ancient ally Thingol at the hands of the Dwarves, they went with Beren to avenge him. Much later, after the deaths of Beren and Lúthien, one of their lords took up the Silmaril that Lúthien had borne, and brought it to Menegroth where Dior now dwelt.
After the end of the First Age, their fate is not clearly known. Much of their land survived the destruction of Beleriand, and as Lindon came under the rule of Gil-galad. Some at least seem to have removed to Eriador, as a note in the Unfinished Tales mentions Green-elves living on the shores of Lake Nenuial during the Second Age. After this, nothing is known of their fate.