The authors agree that this surname derives from the anthroponym of Irish Gaelic origin Niall, linked to roots with possible senses of "champion" and "cloud". F. Miranda further notes other possible etymologies: the alteration of the Latin cognomen Nelius, the aphaeresis —that is, the loss of the initial syllable— of names such as Aniello, or of hypocoristics of Bruno, Ennio, Iginio or Antonio.

V. Blunda goes deeper into the historical trajectory of the name Niall: it was borne by the legendary kings of Ireland, in particular by Niall of the Nine Hostages (4th–5th centuries), the mythical ancestor of the Uí Néill dynasty. Its transmission to the European continent came about through the Irish monks who evangelized Europe during the early Middle Ages, founding monasteries such as Bobbio, Sankt Gallen and Luxeuil.

Miranda describes the geographical distribution of the surname: its main stem is located in Sicily, with a presence in the provinces of Agrigento, Syracuse, Palermo, Trapani and Enna, together with small clusters in Lombardy, Piedmont, Liguria, Veneto and Friuli-Venezia Giulia.