John was the son of
Ubaldo I Visconti and cousin of
Ubaldo of Gallura. When the latter Ubaldo drew up a will in January 1237 at
Silki, John was nominated to succeed him. However,
Enzo, the husband of his Ubaldo's widow
Adelasia of Torres, seems to have taken control of both Gallura and
Logudoro and was granted the title
King of Sardinia by his father, the
Emperor Frederick II. Nevertheless, John was soon in power in Gallura. In 1254, he joined the
Republic of Pisa in her attack on
John of Cagliari. In 1258, the Republic partitioned the
Giudicato of Cagliari amongst her supporters. John annexed a third of it —
Ogliastra,
Quirra,
Sarrabus, and
Colostrai — to Gallura. John subsequently remained mostly on the Italian peninsula, participating in the wars between the
Guelphs and the
Ghibellines on the side of Pisa. He returned to the island in 1274, but was back in Pisa the next year, when he died there. All his possessions passed to the Republic. He married Dominicata, daughter of
Aldobrandino Gualandi-Cortevecchia, but she died in 1259. He was later re-married to Giovanna, a daughter of
Ugolino della Gherardesca, Count of
Donoratico. He was one of Ugolino's few supporters during the factional infighting which plagued Pisa. His son by Ugolino's daughter,
Ugolino, called Nino, succeeded him. ==References==