Giannetti studied in the atelier of Carlo Arienti in Genoa and later in Rome with Francesco Coghetti. He was a frequent exhibitor at the Accademia Veneta and at the International Exhibition in Vienna. In 1874 he moved to Florence to paint The Death of Beatrice which was later exhibited in Naples in 1876. He travelled throughout Europe and while in London met Frederic Lord Leighton. He spent the latter years of his life in solitude executing history and genre paintings in the academic tradition. After his death in 1923 The Palazzo Rosso in Genoa held a retrospective exhibition of his works.