Elendur no doubt lived with his father within the Realms in Exile probably in Arnor. When the Last Alliance of Elves and Men was formed and the war against the forces of Sauron begin, Elendur's role in it is unknown but it is possibly he was involved in it.
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, 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.