Omner was a son of King Mosiah², one of four sons named with his brothers Ammon, Aaron, and Himni (Mosiah 27:34). Before his conversion he was among the unbelievers and went about secretly with his brothers seeking to destroy the church and lead away the people (Mosiah 27:8-10). An angel appeared to the sons of Mosiah while they were rebelling against God, and Omner was converted (Mosiah 27:11).
Omner and his brothers declined the Nephite kingdom and asked their father instead to let them go to the land of Nephi to preach to the Lamanites; Mosiah inquired of the Lord and granted the request. Because none of his sons would accept the throne, the kingdom passed out of Mosiah’s line (Mosiah 28:1-10).
Before going, Omner had a sound understanding, had searched the scriptures, and had given himself to much prayer and fasting, so that he taught with the spirit of prophecy and revelation (Alma 17:2-3). He and his brothers preached among the Lamanites for fourteen years (Alma 17:4). The converted Lamanite king issued a proclamation forbidding his people to harm Omner or the others, granting them free access to preach (Alma 23:1-3). They were beaten, spit upon, stoned, bound, and imprisoned, yet were delivered and rejoiced in their success in converting many (Alma 25:17; 26:29-30).
Omner later went with Alma the Younger to preach to the Zoramites, along with Ammon, Aaron, Amulek, Zeezrom, and Alma’s sons Shiblon and Corianton (Alma 31:6-7). After that mission he returned with them to the land of Zarahemla (Alma 35:14).