His father Lino Nonveiller was a chemical engineer that travelled through Europe and educated Guido and his sister in Rijeka, Vienna and Split.

In 1927, he was introduced to Peter Novak, an early Croatian entomologist, who made a lasting impact on the young boy and stimulated a lifelong passion for insects.

From 1960 to 1962 he worked in Tunisia as plant protection officer, and from 1962 to 1985 as United Nations Food and Agriculture Organization expert in Yaounde, Cameroon.

The same year, Jacques Chirac, then French President, granted him the legal status of former service personnel ("anciens combattants").

Nonveiller was internationally renowned for researching the African and Palaearctic Mutillidae and Bradynobaenidae (Hymenoptera), a leading specialist for several groups of Coleoptera of the Balkans and adjacent areas and a prominent expert in economic entomology and historiography of his time.