At an advanced age, John gave away his wealth to the poor of Genoa and entered the Order of St Dominic. Nothing is known of him before this.
He is best known for his Latin grammar, Summa Grammaticalis, better known as the Catholicon, apparently the first lexicographical work "to achieve complete alphabetization (from the first to the last letter of each word)." This work is made up of treatises on orthography, etymology, grammar, prosody, rhetoric, and an etymological dictionary of the Latin language (primae, mediae et infimae Latinitatis). It was highly respected as a textbook for over a century after its publication, and received both excessive criticism and excessive praise. Erasmus was particularly critical of the work, criticizing it in his works De Ratione Studiorum and Colloquia. Leandro Alberti wrote a defense of the Catholicon in response to these attacks.
Besides the Catholicon, John also wrote Liber Theologiae qui vocatur Dialogus de Quaestionibus Animae ad Spiritum and Quoddam opus ad inveniendum festa mobilia. A Postilla super Joannem and a Tractatus de Omnipotentia Dei have also been attributed to him.