He also notably translated Engelbert Humperdinck's Hänsel und Gretel into English, a version first performed in 1967 and used by opera companies to this present day.

He sang regularly with that company over the next two years in such roles as Alfredo in Giuseppe Verdi's La Traviata, Don José in Georges Bizet's Carmen, Pinkerton in Puccini's Madama Butterfly, Radamès in Verdi's Aida, and the title role in Charles Gounod's Faust.

In 1950 Kelley made his Broadway debut as Magician Nika Magadoff in Gian Carlo Menotti's The Consul at the Ethel Barrymore Theatre.

[3] Kelley became a fixture at the New York City Opera during the 1950s and 1960s, including leading roles in four world premieres — the title role in Robert Kurka’s The Good Soldier Schweik (1958), Reverend Samuel Parris in Robert Ward's The Crucible (1961), Lord Mark in Douglas Moore's The Wings of the Dove (1961), and Ely Pratt in Carlisle Floyd's The Passion of Jonathan Wade (1962).

[2] Other notable NYCO roles for Kelley included Pandarus in William Walton's Troilus and Cressida (1956); the Narrator in the U.S. premiere of Carl Orff's Der Mond (1956); Count Mancini in Ward's He Who Gets Slapped (1959); Mr. Scratch in Moore's The Devil and Daniel Webster (1959) and Méphistophélès in the U.S. premiere of Prokofiev's The Fiery Angel (1965).

The production was notably organized by Lincoln Kirstein and George Balanchine and led by music director Erich Leinsdorf.

[1] His other roles at the Met included Mime in Wagner's Siegfried, Don Basilio in Le Nozze di Figaro, Herod in Richard Strauss's Salome, Prince Shuisky in Mussorgsky's Boris Godunov, and Goro in Madama Butterfly among others.