In 718 he appears as the ally of Chilperic II., king of Neustria, who was fighting against the Austrasian mayor of the palace, Charles Martel; but after the defeat of Chilperic at Soissons in 719 he probably made peace with Charles by surrendering to him the Neustrian king and his treasures.
The Austrasian mayors of the palace succeeded in enforcing their authority in the western as well as in the eastern part, and in re-establishing to their own advantage the unity of the Frankish kingdom.
But the Neustrians threw off the Austrasian yoke and entered into an offensive alliance with the Frisians and Saxons.
It was by means of their horsemen that the Austrasian Franks established their superiority over their neighbours, and in time created the Western Empire anew, while from the word caballarius, which occurs in the Capitularies in the reign of Charlemagne, came the words for knight in all the Romance languages.
In 656, at the moment of his accession to power, Sigebert III., the king of Austrasia, had just died, and the Austrasian mayor of the palace, Grimoald, was attempting to usurp the authority.
Arnulf was one of the Austrasian nobles who appealed to Clotaire II., king of Neustria, against Brunhilda, and it was in reward for his services that he received from Clotaire the bishopric of Metz (613).
Pippin, also an Austrasian noble, had taken a prominent part in the revolution of 613.
These two men Clotaire took as his counsellors; and when he decided in 623 to confer the kingdom of Austrasia upon his son Dagobert, they were appointed mentors to the Austrasian king, Pippin with the title of mayor of the palace.
The ecclesiastical party also abandoned Brunhilda because of her persecution of their saints, after which Clotaire, having now got the upper hand, thanks to the defection of the Austrasian nobles, of Arnulf, bishop of Metz, with his brother Pippin, and of Warnachaire, mayor of the palace, made a terrible end of Brurihilda in 613.
These two tendencies, were destined to strive ~against one another during an entire century (613714), and to occasion two periods of violent conflict, which, divided by a kind of renascence of royalty, were to end at last in the triumphant substitution of the Austrasian mayors for royalty and aristocracy alike.
The death of Grimoald had caused, the loss of this post, yet Ansegisus (Ansegisel), Arnulfs son and Pippins son-in-law, had continued to hold high office in the Austrasian palace; and about 680 his son, Pippin II., became master of Austrasia, although he had held no previous office in the palace.
With Charles Martel begins the great period of Austrasian history.
Faithful to the traditions of the Austrasian mayors, he chose kings for himselfClotaire IV., then Chilperic II.