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 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.
| Judge of Gallura