Prior to deciding on a career in music, Bonelli was a friend of race car driver and later mayor of Salt Lake City, Ab Jenkins.

[1] He soon began actively training with voice teachers, including Arthur Alexander in Los Angeles and with Jean de Reszke and William Valonat in Europe.

His debut role in San Francisco was Figaro in Rossini's Il barbiere di Siviglia, after appearing in Flotow's Martha at the Los Angeles Grand Opera earlier in September 1926.

[3] Seizing the opportunity of a one-year collapse of Chicago Civic Opera, the Met impresario Giulio Gatti-Casazza quickly engaged Bonelli for leading baritone roles in New York.

Bonelli's New York Metropolitan Opera debut came on 1 December 1932 as Giorgio Germont in Verdi's La traviata opposite Rosa Ponselle as Violetta and Tito Schipa as Alfredo.

[3][4] Of his many roles, Bonelli was known best for his Verdi repertory as Giorgio Germont, Di Luna, Renato, Rigoletto and Amonasro, and also for his portrayals of Valentin in Gounod's Faust, Wolfram in Wanger's Tannhäuser, Tonio in Leoncavallo's Pagliacci, Rossini's Figaro, Enrico Ashton in Donizetti's Lucia and Sharpless in Puccini's Madama Butterfly.

American baritone Robert Merrill had stated that Bonelli was his inspiration to study singing, after hearing him perform the Count di Luna at the Met alongside Giovanni Martinelli and Elisabeth Rethberg in 1936.