Mario Janni was born in Rome, and took courses at the Art Institute of Syracuse. His first professional comics work was drawing 'Phantom' ('L'Uomo Mascherato') stories for Spada, as well 'Gigetto' fro Geis in Milan and 'Maghella' for Studio Leonetti. He then worked for Universo, LancioStory, Ediperiodici and Edifumetti. From 1980, he illustrated stories with 'Nick Raider' for Bonelli. Later on, he also took on stories with 'Julia'. In addition, Jannì has worked in infographics at the Ansa agency.