He made his stage debut in 1896 at the Teatro Mercadante in Foggia as Don Carlo di Vargas in Giuseppe Verdi's La forza del destino.
On 19 December 1903, Bonini made his debut at the Teatro di San Carlo in Naples as Michonnet in that house's first staging of Francesco Cilea's Adriana Lecouvreur with Solomiya Krushelnytska in the title role.
He remained committed to that theatre through 1905, portraying such roles as Walitzin/Commissario in Umberto Giordano's Siberia and Johannes Rathenow in the Italian premiere of Ruggero Leoncavallo's Der Roland von Berlin.
He sang at the Teatro Regio di Parma in 1907–1908, portraying such roles as Carlo Gérard in Andrea Chénier, David in L'amico Fritz, Kurwenal in Tristan und Isolde, and Rinaldo in Amica among others.
In 1911–1912 Bonini returned to La Scala where he was seen as Hidraot in Christoph Willibald Gluck's Armide, King Raimondo in Isabeau, and Hans Sachs in Die Meistersinger von Nürnberg.