Eleazar was Aaron's third son by his wife Elisheba. Eleazar became a priest along with his father and three brothers. He married a daughter of Putiel who bore him a son, Phinehas. After his two older brothers, Nadab and Abihu, were killed for making an unholy offering to God, and during his father's lifetime, "he was supervisor over those who had charge of the sanctuary".
When Aaron died at Mount Hor, Eleazar became the high priest. Before Moses died, the Lord instructed Moses to appoint Joshua as his successor, and to "stand before Eleazar the priest and all the congregation". Eleazar served as the the high priest through the rest of Moses' life and throughout Joshua's leadership in taking over Canaan.
He helped in the allotment of Canaan among the twelve tribes of Israel. Eleazar was buried at Gibeah, a town belonging to Phinehas in the hill country of Ephraim. Phinehas succeeded him as high priest. In King David's day, 16 of the 24 priestly houses were descended from Eleazar, including the family of the high priest Zadok.