Like his younger brother Izates bar Monobazus and his mother, Monobazus became a convert to Judaism. He ruled as king of Adiabene after the death of his brother Izates around 55 CE. The date of his death is unknown but he is known to have been alive and on the throne during the First Jewish-Roman War, when he gave aid to the Jewish rebels against the Roman Empire. Two 'kinsmen' of Monobazus, Monobazus and Kenedaeus, fought on the side of the Jews in the battle against Cestius. The 'sons and brothers of Izates the king' were taken hostage to Rome after the war.
The Talmud relates that Monobazus: "dissipated all his own hoards and the hoards of his fathers in years of scarcity. His brothers and his father's household came in a delegation to him and said, 'Your father saved money and added to the treasures of his fathers, and you are squandering them.' He replied, 'My fathers stored up below and I am storing up above... My fathers stored in a place which can be tampered with, but I have stored in a place which cannot be tampered with … My fathers gathered treasures of money and I have gathered treasures of souls...' " King Monobaz also donated handsome gifts to the Temple in Jerusalem. "King Monobaz had all the handles of all the vessels used on Yom Kippur made of gold … He also made of gold the base of the vessels, the rims of the vessels, the handles of the vessels, and the handles of the knives..."