He was born and resided in mainly in Roma. Son of Francesco, a Roman jeweler and mosaicist, part of a family of mosaicists. A 16-year-old Attilio was apprenticed with the Spanish painter Mariano Fortuny at the urging of the painter Nicola Ortis of Perugia. In 1868, Simoneti submitted two paintings to an exhibition at the Brera of Milan: Interior of Kitchen at Trastevere and Gate at via dei Carbonari. At the 1877 Neapolitan Esposizione Nazionale di Belle Arti he displayed a copy of the paintings "L'araldo" and "Il tamburino". In Naples, he made friends and was encouraged by Filippo Palizzi. In 1875, he was one of the founders of the Association of Acquarellisti Romani (Roman Watercolor Painters).
Among his works: After the Dance; exhibited in 1877 in Naples: Un araldo; Un tamburo; Ogni speranza è morta; Via Giuseppe Mancinelli in Palazzuolo Castracelo. He also exhibited at the 1883 Mostra of Fine Arts in Rome, some paintings and watercolors: A governor; Gioia materna; and La filatrice. He painted the period costume drama of L'Ubriaco (1877).
Simonetti had a good relationship with Adolphe Goupil of the Goupil Gallery of Paris, famed for the patronage of impressionism. He died in Rome. The Simonetti family continued the antiquarian business.
- I primi anni di Roma capitale (1870-1878): con 100 illustrazioni By Ugo Pesci, page 421.
- Dizionario degli Artisti Italiani Viventi: pittori, scultori, e Architetti., by Angelo de Gubernatis. Tipe dei Successori Le Monnier, 1889, page 481.
- Attilio Simonetti, pittore e antiquario romano e via Margutta., article by Giovanni Carboni in text: Atelier in Margutta, Cinque secoli di cultura internazionale a Roma; Allemandi, publisher; Valentina Moncada, editor.
- Attilio Simonetti e la Maison Goupil in the catalog of the exhibition La Maison Goupil Il successo italiano a Parigi negli anni dell’impressionismo; Silvana Editoriale, publisher; Paolo Serafini, editor 2013.
- Article Attilio Simonetti in Enciclopedia di Roma dalle origini all’anno 2000; F. M. Ricci, publisher, Milan.
- Goffi Carboni Antiquariato on Via Margutta, Rome.