Third son of Finwe, second son by his second wife Indis the Vanya, and youngest of Finwe’s sons. He was born in Valinor during the ages of Melkor’s Captivity. He married Earwen, daughter of Olwe, ruler of the Teleri who dwelt on the shores of Aman and brother to Elwe (Elu Thingol, King of Doriath). His children were Finrod Felagund, Orodreth, Angrod, Aegnor, and Galadriel.
After the Death of Finwe, Feanor gathered the Noldor to Tuna and moved them with his speech to leave Aman in search of lands and to make war upon Morgoth. Finarfin attempted to calm the Noldor and make them think before they acted. He was unsuccessful, and daring not to leave his people alone to the councils of Feanor, he marched with his brother Fingolfin. Finarfin was most loath to leave Aman, and he and his son Finrod Felagund were in the rear of the host. With them went "many of the noblest and wisest of the Noldor," and they often looked back at the city they were leaving behind. They also carried the most with them from Aman. Being in the rear of the host, he had not participated in the Kinslaying at Alqualonde. After the Prophecy of the North was given by Mandos, Finarfin forsook the march, overcome with sorrow and bitterness, and led those who would follow him back to Valinor. They were pardoned, and Finarfin was given the lordship over the remaining Noldor. However, his sons and daughter marched on with the host of Fingolfin, and with them were left to contend with the Helcaraxe when Feanor stole the ships and burned them at Losgar.
Finarfin is said to be "fairest, and most wise of heart" of Finwe’s sons.
Background beyond the Silmarillion
The character of Finarfin as Finwe’s third son first appears in added portions of the early texts of the Silmarillion, and then at first he is called Finrod. In other texts, he is mentioned in a note to the Lay of the Children of Hurin, and is finally mentioned in the actual story text in the Lay of Leithian. In the Lay of Leithian, he is mentioned as the one who created the insignia on the ring given to Barahir (father of Beren) by Felagund ("snakes with emeralds for eyes, twined and meet beneath a golden crown of flowers, one upholds and the other devours"). In the Silmarillion this is said to be the badge of Finrod Felagund and his house. In the Lay of Leithian, it is the badge of Felagund’s father Finrod (Finarfin).
Unfinished Tales also gives some insight to Finarfin. The section titled "The History of Galadriel and Celeborn" gives this description of Finarfin:
"Finarfin was of his mother’s kind in mind and body, having the golden hair of the Vanyar, their noble and gentle temper, and their love of the Valar… as best he could he kept aloof from the strife of his brothers and their estrangement from the Valar, and he often sought peace among the Teleri, whose language he learned."There is also given this passage a few paragraphs later:
"(Galadriel) was proud, strong, and self-willed, as were all the descendents of Finwe save Finarfin."These two passages reveal at least three things. First is a reason why Finarfin is never mentioned in connection with the quarrels of his older brothers: He did not share their temperament, and preferred not to be involved, so he went to Alqualonde, which also gave him the chance to meet and marry Earwen. Second, it shows us just how "sundered" the speech of the Teleri had become from that of the other Elves of Aman: Finarfin had to learn a new language. Third, it shows that Finarfin was not and would not have been a very useful tool for Morgoth’s designs because of Finarfin’s personality. Finarfin was inclined to seek peaceful ends to situations, and Morgoth was inclined to cause strife.
Finarfin remained under the name Finrod under the second edition of Lord of the Rings.
Sources:
The Silmarillion
Unfinished Tales
Book of Lost Tales 1 and 2
Lays of Beleriand
Shaping of Middle Earth
The Lost Road and other Writings