The earliest account of the origin of the Tosny family is that of the late-11th century Acta Archiepiscoporum Rotomagensium (The Acts of the Archbishops of Rouen), which refers to a 'powerful man', Raoul, son of Hugh de Calvacamp, of illustrious stock, and brother of Hugh, Archbishop of Rouen, active from 942 to 989. He had formerly been a monk at St. Denis, suggesting a French origin for the family. The Archbishop gave Raoul lands at Tosny, taken from the church's holdings. By the early 12th-century, this French family had been given a Norman pedigree, Norman chronicler Orderic Vitalis writing in an interpolation into the Gesta Normanorum Ducum of William of Jumièges, that Roger de Tosny, then Lord of Tosny and Conches, was “de stirpe Malahulcii qui Rollonis ducis patruus...” (of the lineage of Malahulc, uncle of Duke Rollo
Coming from Île-de-France, the Tosnys first based themselves in Normandy in the 10th century to collaborate with the descendants of the Vikings. They formed part of this new elite which appeared around dukes Richard I and Richard II at the turn of the 10th to 11th century. In 991, Raoul I of Tosny witnessed an accord between Duke Richard I and the Anglo-Saxon king Ethelred II. He also participated in the Norman conquest of southern Italy As one of the top Normans, he set out to fight in southern Italy. His grandson Raoul II was at the court of William the Conqueror (1035–1087), and was the Norman standard bearer in 1054.
Narratives, more or less legendary, gathered around the family: the chroniclers report the exploits of Roger I, the Moor-Eater, in Hispania. His wife, Godehildis/Gotelina, was linked to a miracle at Sainte-Foy de Conques.
As with several Norman families (such as the Beaumont), the origin of the house of Tosny's power derived from two sources :