Amadeus was born in Montmélian, Savoie. The legitimate heir of Thomas I of Savoy and Margaret of Geneva, he had however to fight with his brothers for the inheritance of Savoy's lands after their father's death. His brothers Pietro and Aimone spurred a revolt in Aosta Valley against Amadeus, but he was able to crush it with the help of Manfred III of Saluzzo and Boniface II of Montferrat, who were his sons-in-law. Together with his brother, Thomas, he fought against the communes of Turin and Pinerolo, but with uncertain results.