From the first name Giovanni, derived from the Hebrew "Yohanan", consisting of "Yahwè" = God and "hanan" = to be merciful.

The authors agree that Vanni is an abbreviated form of the name Giovanni, arisen by aphaeresis —that is, the suppression of the initial syllable—, a usual phenomenon in the Italian dialects. The result, Vanni, functioned as a popular hypocoristic and gave rise to the surname by the patronymic route, originally designating the "son of Giovanni".

The surname was especially frequent in Tuscany, Umbria and other zones of central Italy, and from this base numerous variants were generated with diminutive, augmentative or affectionate suffixes, such as Vannini, Vannucci, Vannozzi, Vannino and Vannetti, among others.

V. Blunda provides a different regional perspective: he notes that in Sicily the surname has a dialectal character and derives from the Sicilian word vànni, meaning "John", a form that refers to the name of Hebrew root diffused by the Christian devotional tradition. Blunda indicates that its transformation into a surname could have occurred as a patronymic applied to the son of a John prominent in the community.

The surname therefore presents independent origins in different regions of Italy: one linked to the peninsular centre, with irradiation from Tuscany and Umbria, and another of dialectal character typical of Sicily.