How old was Josiah when he became king? Josiah was eight years old when he became king of Judah. The biblical accounts in 2 Kings and 2 Chronicles describe him succeeding his father, Amon, after Amon was assassinated.
Josiah reigned for 31 years, approximately from 640 to 609 BCE. Because he was a child when he took the throne, officials and advisers would have helped administer the kingdom during his early years. The biblical narrative later presents him as a major religious reformer who sought to centralize worship in Jerusalem and remove practices associated with foreign gods.
According to the accounts, temple repairs during the eighteenth year of Josiah's reign led to the discovery of a book of the law. Josiah responded with further reforms and a renewed covenant. He was killed in 609 BCE during a confrontation with Pharaoh Necho II. A frequent mix-up is with Joash, another king of Judah who became king at age seven; Josiah became king at eight.