The son of Tuor and Idril, daughter of Turgon, Eärendil was raised in Gondolin. When Eärendil was seven years old, he escaped the sacking of Gondolin with his parents, living afterwards in Arvernien by the mouth of Sirion. Eärendil later became the leader of the people who lived there, and married Elwing, daughter of Dior the son of Beren and Lúthien. They had two sons, Elrond and Elros.
With the aid of Círdan the Shipwright, Eärendil built a ship, Vingilótë (or Vingilot), which is Quenya for "foam-flower". He sailed this often around the seas west of Middle-earth, leaving his wife behind in Arvernien. At this time Elwing had in her possession the Silmaril that Beren had wrested from Morgoth. News of this came to the sons of Fëanor who were still living, and they attacked the people living in Arvernien, and killed most of them. Elwing, rather than be captured, threw herself with the Silmaril into the sea. The Silmaril was not lost, however. According to The Silmarillion:
For Ulmo bore up Elwing out of the waves, and he gave her the likeness of a great white bird, and upon her breast there shone as a star the Silmaril, as she flew over the water to seek Eärendil her beloved. On a time of night Eärendil at the helm of his ship saw her come towards him, as a white cloud exceeding swift beneath the moon, as a star over the sea moving in strange courses, a pale flame on wings of storm. And it is sung that she fell from the air upon the timbers of Vingilot, in a swoon, nigh unto death for the urgency of her speed, and Eärendil took her to his bosom; but in the morning with marvelling eyes he beheld his wife in her own form beside him with her hair upon his face, and she slept.
Hearing of the tragedy that had befallen in Arvernien, Eärendil then sought after Valinor, aboard the Vingilot with Aerandir, Erellont, and Falathar, and he and Elwing found their way there at last. Eärendil thus became the first of all mortals to set foot in Valinor. Eärendil then went before the Valar, and asked them for aid for Men and Elves in Middle-earth, to fight against Morgoth; the Valar accepted his plea.
Because Eärendil had undertaken this errand on behalf of Men and Elves, and not for his own sake, Manwë forbore to deal out the punishment of death that was due. Also, because both Eärendil and Elwing were descended from a union of Elves and Men, Manwë granted to them and their sons the gift to choose to which race they would be joined (a gift that was further passed to the children of Elrond, who became known as the Half-elven). Elwing chose to be one of the Elves. Eärendil would have rather been one of the Men; however, for the sake of his wife, he chose to be one of the Elves. The Silmarillionsays this:
Now when first Vingilot was set to sail in the seas of heaven, it rose unlooked for, glittering and bright; and the people of Middle-earth beheld it from afar and wondered, and they took it for a sign, and called it Gil-Estel, the Star of High Hope.
The Valar, having listened to Eärendil's plea, went with a mighty host to Middle-earth, and overthrew Morgoth. Eärendil took part in the battle, riding on Vingilot beside Thorondor and the Eagles. He struck down the great dragon Ancalagon and cast him down onto Thangorodrim, the event which, along with the sheer devastation caused by the War of Wrath, led to the Ruin of Beleriand. However, right before the Dagor Dagorath, the Last Battle, Morgoth will escape out the Door of Night to destroy Arda. It is implied Eärendil shall participate in that, alongside every creature in Middle-earth, good and evil.