As an illustrator, Terzi was described as bringing Art Nouveau poster design to a world-class level.
He produced work throughout his life, notably for the Italian poster company Casa Ricordi.
He worked as an illustrator for a Rome daily called La Tribuna Illustrata.
[1] He illustrated Italian versions of Little Lord Fauntleroy and Gulliver's Travels.
His brother, Amedeo John Engel Terzi (1872–1956), was also an artist (illustrator and entomologist specialising in Diptera).