Elendur was born in Númenór and followed his father and his grandfather Elendil in the fleet that was blown to Middle-earth after the Fall of Númenór. Elendur no doubt lived with his father within the Realms in Exile, probably in Arnor.
Elendur was the only son of Isildur to have a role with the army of the Last Alliance, fighting in the Battle Of Dagorlad and accompanied his father in Mordor during the Siege of Barad-Dur. His younger brothers were sent to man Minas Ithil, so Sauron could not escape into the mountains that way. As the eldest son of Isildur, Elendur was high in the confidence of his father; Elendur alone of the sons knew the existence of the Ring in his father's possession and counselled Isildur to turnover the One Ring to the Keepers of the Three Rings. He was slain in the disaster of the Gladden Fields with his father and younger brothers Aratan and Ciryon. He had a squire named Estelmo who survived the massacre. His brother Valandil, who was still a child, had remained in Imladris and so lived to rule Arnor.
In a marginal note in the Unfinished Tales, Aragorn is stated to have resembled this son of Isildur "in body and mind", even though he was not descended directly from him. Elendur himself was noted to have borne a striking resemblance to his grandfather Elendil.
The name Elendur has two possible meanings; the first being "elf servant" and the second being "star servant". It appears to be made from the Quenyan words elen, which means "star", and -ndur, which means "follower" or "servant" (though can be used more affectionately as "friend", though "-ndil" is more commonplace for such a meaning). The name 'Elendur' may have been much in alignment with his grandfather's name Elendil in that the intention of the meaning was to be "elf friend" (from elda, meaning "elf"), but was confused with the word elen, and so conjured the mistranslation of 'Elendil' as "star friend".