The authors agree that this surname derives from the name of Germanic origin Guarnerio, documented from the 10th century in the forms Guarnerius and Warnerus. This name is an adaptation of the Frankish Warinhari, compounded from warin- ("to protect, to defend") and harja- ("army"), with the resulting meaning "he who defends the army". The surname is distributed sporadically throughout Italy, with the greatest concentration in the north-west of the country and in Tuscany.

A. Bongioanni adds that Saint Warnerus —also known as Werner and Garnier—, a 13th-century martyr, is celebrated on 18 May. He also notes that in Piedmont the surnames Garneri, Garnino, Garnerone, Varneri, Verneri and Vernier derive from this same name, while in Veneto the form Guarnièr and variants with initial V- are documented.