In 1915, together with artists Vittorio Costantini, Cipriano Efisio Oppo and Guglielmo Pizzirani, Melli formed the "Gruppo Moderno Italiano" (Modern Italian Group) and in 1918 he contributed to the creation of the magazine and current "Valori Plastici".
[2] Melli resumed his artistic work after World War II, in his Roman flat at Testaccio, where each week he hosted a group of young painters who included Renato Guttuso, Enrico Accatino, and Fausto Pirandello.
In 1957 he published a book of poetry, Lunga favolosa notte (The Fabulous Long Night), and in 1958 the Galleria Nazionale d'Arte Moderna in Rome opened a retrospective exhibition of his work, organised by curators Nello Ponente and Palma Bucarelli.
Exhibited permanently at the Galleria Nazionale d'Arte Moderna of Rome, two works are especially important in his production: La casa rossa (The Red House) (1923), a figurative painting that seems a precursor of Edward Hopper's style and much of the American production; and the sculpture Signora dal Cappello Nero (Lady with Black Hat) (1913), this too an anticipation of a parallel tridimensional experimentation by Italian artist Umberto Boccioni.
[4] Another work of profound intensity was Melli's last, dramatic self-portrait, painted the same month of his death and currently kept at the Portrait Gallery of Palazzo Pitti, in Florence.