The Valar had attempted to fashion the world for Elves and Men, but Melkor continually destroyed their handiwork. After he destroyed the two lamps that illuminated the world, the Valar moved to Aman, a continent to the west of Middle-earth, where they established their home called Valinor. Yavanna created Two Trees that illuminated Valinor and left Middle-earth to darkness and Melkor. Soon after, stars created by Varda began to shine and the Elves awoke. The elves originally formed three groups: the Vanyar, the Noldor, and the Teleri, though some elves were captured and enslaved by Melkor, eventually to be bred into orcs. Knowing the danger the Elves were in, the Valar decided to fight Melkor to keep the Elves safe. After defeating and capturing Melkor, they invited the Elves to live in Aman. Many Elves travelled to Aman, while others refused and still others stopped along the way, including the Elves who later became the Sindar, ruled by the Elf King Thingol and Melian, a Maia. Of the three tribes that set out, all of the Vanyar and Noldor, and many of the Teleri reached Aman.

In Aman, Fëanor, son of Finwë, King of the Noldor, created the Silmarils, jewels that glowed with the light of the Two Trees. Melkor, who had been held in captivity by the Valar, was eventually released after feigning repentance. Upon release, Melkor deceived Fëanor into believing that his eldest half-brother Fingolfin was attempting a coup against Finwë. This rift led to the banishment of Fëanor from the Noldor city Tirion, and Fëanor thereafter created the fortress Formenos to the North of Tirion. Finwë moved to Formenos to live with Fëanor, his favorite of three sons, and there they safely kept the Silmarils. After many years, Fëanor traveled to Tirion to make amends with Fingolfin, while Finwë stayed at Formenos. While making amends, Melkor destroyed the Two Trees with the help of Ungoliant, a dark spider Melkor found in Avathar, on the Southeast side of Aman. Together, Melkor and Ungoliant then escaped to Formenos, killed Finwë, stole the Silmarils, and fled to Middle-earth. Melkor kept the Silmarils and banished Ungoliant, later attacking the Elvish kingdom of Doriath. He was defeated in the first of five battles of Beleriand, however, and barricaded himself in his northern fortress of Angband.

Fëanor and his sons swore an oath of vengeance against Melkor – and against anyone who withheld the Silmarils from them, even the Valar. Fëanor persuaded most of the Noldor to pursue Melkor, whom Fëanor renamed as Morgoth, into Middle-earth. Fëanor's sons seized ships from the Teleri, attacking and killing many of them, and left the other Noldor to make the voyage by foot. Upon arriving in Middle-earth, the Noldor under Fëanor attacked Melkor and defeated his host, though Fëanor was slain by Balrogs. After a period of peace, Melkor attacked the Noldor but was again defeated and besieged. Nearly 400 years later, he broke the siege and drove the Noldor back.

After the destruction of the Trees and the theft of the Silmarils, the Valar had created the moon and the sun. At the same time, Men awoke, some of whom later arrived in Beleriand and allied themselves with the Elves. Beren, a man who had survived the latest battle, wandered to Doriath, where he fell in love with the elf Lúthien, the king's daughter. The king sought to prevent their marriage by imposing what he believed an impossible task: retrieving one of the Silmarils from Melkor. But together, Beren and Lúthien embarked on this quest. Sauron, a powerful servant of Melkor, imprisoned Beren along the way; but with Lúthien's help he escaped, crept into Melkor's fortress, and stole a Silmaril from Melkor's crown. Having achieved the task, the first union of man and elf was formed, though Beren was soon mortally wounded and Lúthien also died of grief. However she convinced the Vala Mandos to revive Beren and herself, though she had to renounce her immortality.

The Noldor, seeing that a mortal and an elf-woman could infiltrate Angband, perceived that Melkor was not invincible. They attacked again with a great army of Elves, Dwarves and Men. But they were deceived by Melkor, who had secretly darkened the hearts of many of the men. Thus it was that the Elvish host were utterly defeated, due in part to the treachery of some Men. However, many Men remained loyal to the Elves and were honoured thereafter.

None received more honour than the brothers Húrin and Huor. Huor died in battle, but Melkor captured Húrin, and cursed him to watch the downfall of his kin. Húrin's son, Túrin Turambar, was sent to Doriath, leaving his mother and unborn sister behind in his father's kingdom (which had been overrun by the enemy). Túrin achieved many great deeds of valour, the greatest being the defeat of the dragon Glaurung. Despite his heroism, however, Túrin was plagued by the curse of Melkor, which led him unwittingly to murder his friend Beleg and to marry and impregnate his sister Nienor, whom he had never met before, and who had lost her memory through Glaurung's enchantment. Before their child was born, the bewitchment was lifted as the dragon lay dying. Nienor, realizing what grew within her, took her own life. Upon learning the truth, Túrin threw himself on his sword.

Huor's son, Tuor, became involved in the fate of the hidden Noldorin kingdom of Gondolin. He married the elf Idril, daughter of Turgon, Lord of Gondolin (the second union between Elves and Men). When Gondolin fell, betrayed from within by Maeglin, Tuor saved many of its inhabitants from destruction. All of the Elvish kingdoms in Beleriand eventually fell, and the refugees fled to a haven by the sea created by Tuor. The son of Tuor and Idril, Eärendil the Half-elven, was betrothed to Elwing, herself descended from Beren and Lúthien. Elwing brought Eärendil the Silmaril of Beren and Lúthien, and using its light Eärendil travelled across the sea to Aman to seek help from the Valar. The Valar obliged; they attacked and defeated Melkor, completely destroying his fortress Angband and sinking most of Beleriand; and they expelled Melkor from Arda. This ended the First Age of Middle-earth. The last two Silmarils were taken by Fëanor's surviving sons Maedhros and Maglor. However, Maedhros killed himself by leaping into a fiery chasm with a Silmaril while Maglor threw his into the sea and spent the rest of his days wandering along the shores of the world, singing his grief.

Eärendil and Elwing had two children: Elrond and Elros. As descendants of immortal elves and mortal men, they were given the choice of which lineage to belong to: Elrond chose to belong to the Elves, his brother to Men. Elros became the first king of Númenor and lived to 500 years old, being given an extended life in return for choosing to be a Man.