Dagobert assigned the education of Sigebert to Pepin of Landen, who was the mayor of the palace in Austrasia under his father Chlotar II, until 629.

Instead he had put Sigebert under the tutelage of Adalgisel as mayor of the palace and the Bishop of Cologne Saint Cunibert as regent, while keeping Pepin in Neustria as hostage.

It was under Seigbert's reign that the mayor of the palace began to play the most important role in the political life of Austrasia, and he has been described as the first roi fainéant—do-nothing king—of the Merovingian dynasty.

Grimoald allowed the young king to stand at the head of the army trying to quell the rebellion, but was defeated by Duke Radulph.

Though ineffective as a king, Sigebert had become a pious adult under the tutelage of Pepin and later Saint Cunibert and lived a life of Christian virtue.

[6] In 656, after the death of Sigebert, Grimoald attempted to usurp the throne of Austrasia and had the young Dagobert (who was seven years old at the time) tonsured and sent to a monastery in Ireland.

Grimoald's son Childebert was proclaimed King of Austrasia in 656, but the reign was short-lived as he was deposed after seven months in 657 and both he and his father were killed in a revolt.