The authors agree that the surname is of Germanic origin, although they differ in their reading of the etymon. E. Rossoni holds that both Mallardi and its variant Mallardo derive from the medieval Germanic name Malhard, a contracted form of Magilhard, compounded from magin ("strength") and hard ("hard"), with the sense of "very strong" or "very hard", a name probably borne by ancestors who came to Italy in the retinue of the Suebi.

V. Blunda, by contrast, breaks down the compound as malo ("assembly, ritual commitment") and hardh ("hard, valiant"), with the meaning "the strong one of the assembly" or "the valiant one of the commitment", in reference to the assembly of the free people, a central institution of political and judicial life in ancient Germanic legal culture.

According to Rossoni, Mallardi has its main core in Puglia, especially in the Bari area, with an additional presence in the Foggia area, in Taranto and Laterza, and lesser areas in Trieste and Florence. The variant Mallardo is concentrated mainly in the Naples area —with municipalities such as Giugliano in Campania, Villaricca and Marano di Napoli— and also has a presence in Avellino and in Puglia. Blunda further notes a presence of the surname in Sicily.