Arnoul was the 29th. Bishop of Metz, in 612. He was canonized by the Church, Saint Arnoul. He became the Mayor of the Palace of Austrasia, and tutor of Dagobert. In the year 614, when Clotaire II had had Brunehaut killed, he remained the only descendant of the sons of Clovis alive. But he is only a toy in the hands of the Franc aristocracy both lay and ecclesiastic. At the head of each of the three ancient kingdoms, Austrasia, Neustria and Burgundy, the Major Domus [Mayor of the Palace] gains progressively greater importance. On 18 October 614, Clotaire II signed the Edict of Paris which in 27 articles, essentially formed the basic power structure for the Council of Bishops and the Assembly of the Greats [nobles].
In 623, Clotaire II was pushed by the Bishop of Metz and also Pepin [Le Vieux de Landen] , the Mayor of the Palace to give Austrasia its own King. Thus, Clotaire II's son Dagobert became King of Austrasia and under the tutelage of Arnoul.