American baritone Robert Mellon has been praised not only for his "glorious voice that burst[s] out brimming with life and vigor," but also for having "immense skill as an actor."

In the 2023-2024 season he will sing George in Of Mice and Men in a return to Livermore Valley Opera. House debuts this season will be with Winter Opera Saint Louis as Leporello in Don Giovanni, Detroit Opera as Terry in Breaking the Waves, and Florida Grand Opera as Tonio in Pagliacci. Mr. Mellon will also sing the title role in an adaptation of Monteverdi's Ulysseswith In Series Opera.

In the 2022–2023 season, he debuted at Opera Tampa as Tonio, Lyric Opera of Kansas City as Escamillo in Carmen and Tulsa Opera as Taddeo in L'italiana in Algeri. He returned to Pensacola Opera to sing Marcello in La bohèmeand Syracuse Opera/Tri-Cities Opera for the title role in Le nozze di Figaro. He made a role debut as Dandini in La Cenerentolawith Opera Maine, where he previously performed Figaro and Papageno in Die Zauberflöte.

The 2021–2022 season saw his return to Opera de Oviedo in role debuts as Marcello and Gubetta in Lucrezia Borgia, having previously performed with the company as Simone in Eine Florentinische Tragödie and Tonio in Pagliacci. He debuted with Opera Philadelphia as Marullo in Rigolettoand Pensacola Opera as Papageno. With In-Series Opera, Mr. Mellon sang the role of Iago in Otello. He returned to Union Avenue Opera for the title role of Falstaff, where he sang the "honor aria" with an "authority and comic force" that made it a "genuine showstopper." That performance as Falstaff won him the St. Louis Theater Circle Award for Outstanding Achievement in Opera.

In previous seasons, Mr. Mellon performed with San Diego Opera as Schaunard in La bohème, Las Vegas Opera as Malatesta in Don Pasquale, Union Avenue Opera as Figaro in Il barbiere di Siviglia, and Syracuse Opera in the roles of Don Alfonso in Così fan tutte and Leporello in Don Giovanni. He sang in the world premiere of Dear Erich with New York City Opera and performed as Willem/Usher in the American premiere of Glass's The Trial with Opera Theatre of Saint Louis. In a double bill with Livermore Valley Opera, he sang the title role of Gianni Schicchi and delivered a performance of Simone in Eine Florentinishce Tragödie that won the company the American Opera Award. According to the San Francisco Chronicle, he sang Simone in "robust, dark-hued tones that consistently rang out at the forefront of the musical texture...with a steely vocal edge that never interfered with the beauty and flexibility of his singing."

As a guest artist in 2014 with his alma mater, Manhattan School of Music, he performed the title role of Bloch's Macbeth in the American premiere of that work in the original French, a performance where his "dark baritone [was] full and fresh and quick with dramatic fire." Among his other roles are Sam in Trouble in Tahiti and Pizarro in Fidelio.

Concert work includes the Mozart and Duruflé Requiems, Dvorák's Te Deum, Stravinsky's Pulcinella, Rossini's Petite Messe Solonelle, Bach's Magnificat, and Mussorgsky's Songs and Dances of Death. In a concert performance of La Belle et le Bête with Present Music he sang the roles of Le Père, Ludovic, and L'Usurier.