The surname Magno and its many variants belong to an ancient family of surnames in which different historical, linguistic and territorial roots converge.

According to the Italian linguist E. De Felice, the surname may derive directly from the Latin name Magnus, used in Roman times as a supernomen or signum, based on the adjective magnus, that is: "great", "important", "illustrious" or "powerful". On this reading, the surname would have arisen initially as an honorific byname linked to physical, social or moral characteristics.

De Felice also notes other possible origins. In certain cases, especially for forms such as Magnóni, it could be a matter of nicknames derived from magnare, a dialect variant of mangiare ("to eat"), probably alluding to a person of great appetite or bulk. In Lombardy, moreover, some lineages could be related to the place name Magno, in the province of Brescia.

E. Rossoni stresses that Magni is very frequent in central and northern Italy, while Magnini has important cores in Lombardy, Tuscany, the Marche and Umbria. The form Magno, by contrast, appears with a greater presence in southern Italy. According to Rossoni, these surnames derive mainly from the Latin cognomen Magnus, whether directly, through hypocoristic forms, or by way of place names related to that name. In other cases, the origin is linked to the term "magno" understood as "great" or "eminent".

To these linguistic roots may be added a possible religious influence. The name Magno was associated in Italy with various medieval saints, among them Saint Magnus, venerated especially in regions such as Lazio and Piedmont. As happened with many Italian surnames, local devotion to particular saints could influence personal names as well as family and place names.