Born in Florence in 1933, Guarnieri started painting in 1953 alongside his musical activity.
His first solo show was held in 1960 at Galerie de Posthoorn in The Hague. In 1966 he was invited to the Venice Biennale and the seminal exhibition Weiss auf Weiss at the Kunsthalle, Bern. In 1967 he exhibited at the Paris Biennale and participated in the shows of Nuova Tendenza. Numerous important solo shows were dedicated to the artist over the years.
He took part in several national and international shows linked to Analytic Painting and New Painting. Amongst these are Geplante Malerei, Concerning Painting, Konkrete Kunst, La peinture Italienne Aujourd’hui, Bilder ohne Bilder, Begegnugn mit Italien, and I colori della Pittura.