Little is mentioned about Maedhros's youth in The Silmarillion. Born to Fëanor and Nerdanel during the Years of the Trees in Aman, he was the eldest of their seven sons (his brothers were Maglor, Celegorm, Caranthir, Curufin, and twins Amras and Amrod). With their father, they often travelled far and wide in Valinor. During this time Maedhros befriended Fingon, son of Fingolfin, for whom Fëanor had no love.
Following his father’s banishment from Tirion, Maedhros lived in Formenos with his family. They returned to Tirion, however, after Maedhros brought tidings of Finwë’s murder and the theft of the Silmarils to his father and Manwë in Y.T. 1495. Fëanor’s fiery words led the Noldor to Middle-earth and the Fëanorians to swear their father’s terrible oath to pursue anyone who kept the Silmarils from their possession.
Maedhros participated in the Kinslaying at Alqualondë and stood aside at the burning of the ships at Losgar. When Fëanor and his sons secretly sailed to Middle-earth, Maedhros was shocked when he realised that they would not return for Fingolfin and his host.
Although Fëanor was killed in the Dagor-nuin-Giliath in Y.T. 1497, Morgoth's forces suffered a crushing defeat. He sent peace emissaries and Maedhros agreed to treat with them. He brought more forces than had been agreed to the parley — for Maedhros was not fooled by Morgoth’s peace offers, but unknown to him, Balrogs were among Morgoth’s party, and the Elven company was overwhelmed. Maedhros was taken captive and hung by the wrist of his right hand upon Thangorodrim in great pain. For many years, he languished there while Fingolfin brought his hosts into Middle-earth. In Y.S. 5, Fingon found him, but Maedhros begged his friend to end his torment by shooting him with his bow. However, with the help of Thorondor, Fingon freed him by cutting off Maedhros’s right hand. This daring rescue, along with Maedhros’ repentance for the desertion of Fingolfin's hosts in Araman and relinquishment of his claim as Finwë’s heir to kingship over all the Noldor in favour of his uncle (which last caused the Fëanorians to be known as “the Dispossessed”), did much to repair the ill feelings between the
House of Fingolfin and the
House of Fëanor.
His brothers, however, were not all pleased by their eldest brother’s actions, and Maedhros, sensing that they would cause feuds with their kinsmen, moved them out of Mithrim and to the lands around the Hill of Himring, which became known as the March of Maedhros. A secondary purpose in relocating was the desire to take up the responsibility to defend the area that was in most danger of being attacked by Morgoth. Keen on peace and unification, Maedhros on his part remained in friendship with the houses of Fingolfin and Finarfin. Allied with Fingolfin, he won the battle of Dagor Aglareb and set the Siege of Angband. The siege was broken, however, in the Dagor Bragollach in which many Elven kingdoms were destroyed. Due to Maedhros's valour and deadly skill with the sword, Himring was successfully defended, though it was surrounded by the enemy. This led many of the survivors from East Beleriand and Dorthonion to rally to Maedhros. He would be the first Noldor Lord to recapture lost lands when he regained the pass of Aglon and closed it to the hosts of Angband.
Taking hope upon hearing the deeds of Beren and Lúthien, he gathered his brothers, and united with other Elven Houses to create the Union of Maedhros, an alliance of Elves, Men, and Dwarves to drive the Orcs from Beleriand and lay siege to Morgoth’s fortress of Angband. Under his leadership, the Union won several battles and regained the territory lost in the Dagor Bragollach. When the joint attack on Angband itself was to be launched, Maedhros was delayed due to the treachery of an Easterling, Uldor the Accursed, who was a spy of Morgoth in the service of Caranthir, and the forces of the Union were utterly destroyed in the Nírnaeth Arnoediad. Himring was taken by the Orcs and the Sons of Fëanor were wounded. They retreated to Mount Dolmed, and eventually came to live with the Nandor in Ossiriand.
During Y.S. 504 — 505, the brothers learnt of the possession of the Silmaril recovered by Beren and Lúthien in the hands of Dior, the new King of Doriath. Maedhros restrained his brothers’ urge to attack, and instead, sent a message to Dior demanding that he yield the Silmaril to them, but Dior ignored it. Celegorm’s words convinced the Fëanorians to launch an assault. Thus Doriath was destroyed, Dior was killed, and the brothers emerged victorious, but the brothers Celegorm, Curufin and Caranthir were slain and the Silmaril was not recovered. Upon learning that Celegorm’s servants had left Dior’s twin sons, Eluréd and Elurín, to starve in a dark forest, Maedhros went on a long search for them, but it proved to be fruitless.
Maedhros and his surviving brothers then dwelt on Amon Ereb in East Beleriand. When they heard that Elwing, who had escaped from Doriath with the Silmaril, was now living at the Havens of Sirion. Maedhros, repenting of his deeds at Doriath, counselled against trying to regain the jewel by force. But the unfulfilment of the oath came to torment the brothers heavily, so they sent messages of friendship but with firm demands to surrender the Silmaril. However, the people refused, arguing that they could not negotiate while their leader and Elwing's husband, Eärendil, was away at sea. In Y.S. 532, the Fëanorians attacked Sirion — but Elwing cast herself and the jewel into the sea and they did not gain what they sought. Elwing was ultimately rescued by the power of Ulmo and reunited with Eärendil in the West. Eärendil and Elwing's sons, Elrond and Elros, Maedhros and Maglor took captive, but treated them gently and kindly.
After the War of Wrath, Maedhros and Maglor, the last of the sons of Fëanor, told Eönwë that the remaining two Silmarils captured from Morgoth should be given to them, but Eönwë replied that the Silmarils would not suffer them to hold them and that the brothers had to face judgement from the Valar in Aman. Maglor was willing to listen, but Maedhros reminded Maglor that in their oath, they had sworn that none, even the Valar, could release them from their oath, and because of this, it would curse them into committing evil deeds in Aman. Resigned, the brothers stole the Silmarils, but the jewels burned their hands because of all the evil deeds they had committed. Unable to endure the suffering, Maedhros and Maglor killed themselves: Maedhros threw himself and his Silmaril into a fiery chasm of the Earth, while Maglor threw himself and his Silmaril into the sea. (However, in the published Silmarillion, here based on 1930s texts, only Maedhros kills himself, Maglor casting his Silmaril into the sea and never returning to his folk, wandering along the coast and lamenting his loss and pain instead.)
In Aman, he was of the Noldorin line for kingship — hence his father-name, Nelyafinwë, which was Quenya for "Finwë the third [in succession]" — but unlike his royal kin, Maedhros had auburn hair inherited from his maternal grandfather, Mahtan, to whom Maedhros was said to be alike in face and disposition. He was mostly referred to as Maitimo — his mother-name for "well-shaped one", for he was noted for his comeliness, but was known as Russandol, his epessë for "copper-top", to his friends and family. His tremendous height earned him the appellation the Tall.