Piatti studied at the Zürich Kunstgewerbeschule from 1937 and had an apprenticeship 1938–42 with the Fretz Bros, Zürich. He opened his own studio in 1948, and later also one in Paris. He was a successful poster designer with an international reputation, who worked in a clear personal style. Was also involved in publicity campaigns and for 30 years was responsible for the artistic and typographic design and publicity for the German publishers DTV. White covers with black type (Akzidenz Grotesk) and mostly colourful illustrations. DTV founded the Celestino Piatti Prize for graphics in publishing (1983). Piatti worked for the Swiss encyclopaedia publishers Mengis + Zier and for Ciba AG in Basel, as well as the Swiss Pavilion at the 1967 Montreal Expo. From the mid-60s he became socially engaged, designing many posters for Caritas Germany (1967–2005) and socio-critical illustrations. Later he turned to fine art: oil paintings, watercolours, drawings and prints.