Born in Savona, and active in Genoa, he constructed scenography for the theatre, and cabinets with lively caricatures, which he also engraved.
He also painted in the church of Santa Teresa in Genoa, and was a follower of Benedetto Luti, whose school he had frequented when in Rome.
He was also a good fresco-painter; his works are in the choir of the Conventual church in Casale Monferrato, where he added figures to the quadratura of Giuseppe Natali.
Nothing can be more amusing than his masks, representing quarrels, dances, and such scenes as form the subjects of comedy.
Giovanni's son, Carlo Giuseppe Ratti, was an artist and art biographer.