Arnout commanded one of the fleets which left on the First Crusade in 1096.
His fleet presumably carried the army of Hugh, Count of Vermandois, since the other crusader armies travelled by land.
He apparently survived the crusade and was at Aachen in 1115 with Emperor Henry V at an Easter celebration, when his fingers began to bleed, a portent of shedding blood through disputes with the princes.
Arnout was married but the name of his wife is unknown.
He and his wife had at least three children: Upon his death, Arnout was succeeded by his son and namesake as Count of Aarschot.