While yet an infant, he was saved from the general massacre commanded by Athaliah of the family by his aunt Jehosheba, and was apparently the only surviving descendant of David (2 Chronicles 21:4, 17). His uncle, the high priest Jehoiada, brought him forth to public notice when he was eight years of age, and had Jehoash crowned and anointed king. Athaliah was taken by surprise when she heard the shout of the people, "Long live the king;" and when she appeared in the temple to challenge this coup, Jehoiada commanded her to be led forth to death (2 Kings 11:13-20).

While the high priest lived, Jehoash favored the worship of Yahweh and observed the law; but on his death Johoash was led into supporting other gods; Zechariah, the son and successor of the high priest, was put to death. For these deeds, the author of the Books of Kings believed Jehoash brought down on the land the judgement of God, and it was oppressed by the Aramean invaders. He is one of the three kings omitted by Matthew (1:8) in the genealogy of Jesus Christ, the other two being Ahaziah and Amaziah. He was buried in the City of David (2 Kings 12:21).