He was the son and successor of Marianus II and reigned initially under the tutelage of Tosorat Uberti, a Pisan nobleman.

Nino Visconti of Gallura having been deposed in 1288, John was the only judge and Arborea the only Judicate left on the island of Sardinia.

In 1300, he ceded (or sold) to Pisa the third of Cagliari which he ruled, the silver mines, and, perhaps, part of the judicial demesne.

This last – the alienation of public land – released the people to revolt (bannus consensus) and they did so, executing John and cutting out his tongue.

He married Giacomina (died 12 February 1329), daughter of Ugolino della Gherardesca, in 1287, on the advice of his father, though he already had sons through a liaison with Vera Cappai, of Villasalto.