Throughout her reign, Benedetta and her husbands — Lamberto Visconti (1220–1225), Henry of Capraia (1227–1228), and Rinaldo Glandi (1230–1232) — exercised the government nominally on his behalf, though his mother ruled also in her own right.
In 1230, Ubaldo of Gallura invaded Cagliari, but the Gherardeschi of Pisa repulsed him in the name of Benedetta and the young William.
Benedetta died late in 1233 or early in 1234 and the Giudicato of Cagliari was divided between several powerful Pisan families.
His reign, however, was consequently peaceful, though he did make war on the Visconti of Gallura until 1244 with the support of Ranieri della Gherardesca di Bolgheri, second husband of Agnes.
In 1239, he made a treaty with Leonard, Archbishop of Cagliari, but he was but a pawn in the Pisan game and his writ lacked any value.