Born to an Italian family in Lima, Peru in 1931, Agnoli moved to Italy in the years immediately following the Second World War. He initially trained as a painter, having studied with Sironi, before embarking on a degree in Architecture from the Politecnico di Milano in 1949. Upon his graduation in 1959 he was an Assistant to Gio Ponti and Carlo De Darli which laid the foundations for a lifelong career in industrial design of both furniture and lighting. He went on to collaborate with some of the best known furniture companies in the world such as Arflex, Oluce, Cinova, Lema, Molteni, Pierantonio Bonacina, Polrona Frau, Schiffini, and Ycami.
Agnoli did not have a professional studio, rather he embedded himself on the sites of the firm he was collaborating with, developing his designs and pieces in conjunction with the technicians and executives there.
His work was globally recognised and he was nominated for two "Compasso d'Oro" prizes and a gold medal at the 1986 Chicago Neocon. Pieces of his design are kept in the permanent collection of the Museum of Modern Art (MoMa) in New York.
He died in Milan in 2012.