According to this source, Arnulf's father was a certain Arnoald, who in turn was the son of a nobilissimus Ansbertus and Blithilt (or Blithilde), an alleged and otherwise unattested daughter of Chlothar I.
There is no direct record of their parents, but it has been suggested that she was a daughter of Arnoald, Bishop of Metz, son of Ansbertus.