Boniface was the third son of William V of Montferrat and Judith of Babenberg, born after his father's return from the Second Crusade. He was a younger brother of William "Longsword", Count of Jaffa and Ascalon, and of Conrad I of Jerusalem. His youthful exploits in the late 1170s are recalled in the famous "epic letter", "Valen marques, senher de Monferrat", by his good friend and court troubadour, Raimbaut de Vaqueiras. These included the rescue of the heiress Jacopina of Ventimiglia from her uncle Count Otto, who was intending to deprive her of her inheritance and send her to Sardinia. Boniface arranged a marriage for her. When Albert of Malaspina (husband of one of Boniface's sisters) abducted Saldina de Mar, a daughter of a prominent Genoese family, Boniface rescued her and restored her to her lover, Ponset d'Aguilar. Like the rest of the family, he also supported his cousin Frederick I Barbarossa in their wars against the independent city communes of the Lombard League.