Celegorm the Fair was the third of the seven sons of Fëanor. The most ambitious of the seven, he followed the oath of his father with the greatest ardour, and this led him to his destruction.
In Valinor, Celegorm became a great hunter, and had the friendship of Oromë, often hunting with the Vala or visiting his house. From Oromë, Celegorm gained great knowledge of birds and beasts, and he learned to understand their tongues, and he gained also another gift, Huan the great hound. He also had great friendship with his cousin Aredhel, the daughter of Fingolfin.
After the Darkening of Valinor, he stood in the court of Tirion with his father and his six brothers, and swore to the Oath of Fëanor. With that, he marched with the Noldor from Valinor and returned to Middle-earth as the Moon rose for the first time. The faithful hound Huan accompanied Celegorm into exile.
After the battle, in which his father Fëanor died, he journeyed to the land of Himlad in the eastern regions of Beleriand, and there took up his abode with his younger brother Curufin. Celegorm and Curufin together claimed the land between the rivers Aros and Celon, and they fortified the Pass of Aglon in the north against the forces of Morgoth. During this time, the two were close in friendship with their brother Caranthir, who dwelt across the valley of the river Gelion in the land of Thargelion, and often went hunting with him.
The land of Himlad was held for more than 450 years by Celegorm and his brother, but in the Dagor Bragollach, Morgoth's armies broke the defence of the Pass of Aglon, and overran Celegorm's lands. With his brother Curufin, he was forced to flee, and they journeyed south and west until they came to Finrod's halls in Nargothrond.
Finrod received his cousins warmly, and for a time Celegorm and Curufin dwelt happily in Nargothrond, hunting the orcs and wolves that dared to cross the Guarded Plain. They were at that time mighty lords, and their power and influence in Finrod's domain grew.
Before many years had passed, though, Beren came out of Doriath seeking Finrod's help in his quest for the Silmaril. The Oath of Fëanor bound Celegorm to defy any that sought a Silmaril, but Finrod was also bound by an oath, to Beren's father Barahir, to lend aid in the quest, and so he departed from Nargothrond, leaving it in the keeping of his brother Orodreth. Celegorm and Curufin exercised their influence after the departure of Finrod, however, and during this time they were effectively the rulers of Nargothrond.
While out hunting on the Guarded Plain, they discovered Lúthien, who having escaped from her father in Doriath was seeking for Beren. Celegorm saw that to be wedded to the daughter of one of the greatest kings in Beleriand would be a great source of power, and so he tricked Lúthien into returning to Nargothrond with him. Once there, he imprisoned her and sent false messages to Thingol, pursuing his suit.
From Lúthien, they learned that Beren and Finrod had been captured by Sauron and imprisoned in his fortress at Tol-in-Gaurhoth. They made no attempt to rescue them, believing that the death of Finrod would further their own power in Nargothrond. Celegorm's hound, Huan, disobeyed his master, and help Lúthien to escape from the brothers, leading her away into the north after Beren.
Though he later returned to Celegorm, their trust was diminished. While he was away from Nargothrond, Huan had aided in the defeat of Sauron in the north, and the destruction of Tol-in-Gaurhoth. Many prisoners of Sauron, who were released when his tower was destroyed, returned to Nargothrond and reported the fate of Finrod. So the lies that Celegorm and Curufin had told in pursuance of power were exposed, and the people turned back to their rightful king, Orodreth. Celegorm and Curufin were exiled from Nargothrond, but their deeds were repudiated by their people, who had come with them from Himlad, and so they journeyed friendless in Beleriand.
After their expulsion from Nargothrond, the brothers journeyed to the north and east, seeking again the lands where they had once ruled, and especially Himring, where their elder brother Maedhros was still lord.
As they travelled beside the eaves of Brethil, they discovered Beren and Lúthien returning from the north, and attacked them. In defence of Lúthien, Huan the hound deserted Celegorm and fought against him. Curufin lost his horse in that fight, and the brothers were forced to ride away eastwards together on Celegorm's steed. Journeying on through Dimbar and Nan Dungortheb, they came at last to the lands of Maedhros.
Celegorm was not to abide there long, for only a few years after their arrival, Maedhros united the Elves of Beleriand, and the great battle known as the Nirnaeth Arnoediad took place. Celegorm marched into the north with his brothers, and was wounded in the battle, but Uldor the Accursed betrayed the Elves and turned against them, and so the host of Maedhros was broken and scattered. Celegorm fled with his brothers to the lands below Mount Dolmed, in the far east of Beleriand.
There they dwelt, a broken and wandering people, for some thirty years. In that time, Beren and Lúthien dwelt in the far south, on the island of Tol Galen in the River Adurant, and with them was the Silmaril that they had recovered from Morgoth's crown. While their oath bound the brothers to recover the jewel, none dared assail that hallowed island, and so they waited.
Eventually, Beren and Lúthien passed away, and the Silmaril was taken to Dior, Thingol's heir, in Doriath. Now the sons of Fëanor sent demands to Dior for the return of the jewel, but Dior disregarded them. So the brothers formed an army and assaulted the halls of Menegroth, and there Celegorm was slain by Dior, though Dior also perished, as did Curufin and Caranthir.
The literal meaning of his name seems to have been 'swift-hasty', but its temporary change to Celegorn and back may suggest that Tolkien did not intend to keep this meaning. (The History of Middle-earth Volume 5, The Lost Road and Other Writings III The Etymologies).