He was only thirteen years of age when he succeeded and of ill health. However, the loyalty of the nobility to his father's memory preserved the peace during his minority. He married Waldrada, daughter of the Lombard king Wacho and his stepsister (a sister of his father's second wife). This marriage fortified the alliance betweent Austrasia and Lombardy.
Nevertheless, Theudebald could not hold on to the conquests of his father in the north of Italia. The Byzantine Emperor Justinian I sent an army under the command of Narses in 552 and, like his father before him, Theudebald avoided direct confrontation with it.
After a prolonged sickness and prostration, he died in 555. His realm passed finally outside of the family of Theuderic I and was united to the kingdoms of his great-uncle Clotaire I, who would soon become king of all the Franks.