Making his debut with the New York City Opera in 1954, he sang 33 roles with them until 1972, returning in 1983 for performances as Danilo in The Merry Widow.
In 1967, Reardon created the role of Orin Mannon (the equivalent of Orestes in Aeschylus' Oresteia) in the world premiere of Marvin David Levy's Mourning Becomes Electra.
[2] He co-starred with Phil Silvers on Broadway in the Jule Styne musical Do Re Mi, introducing the standard song "Make Someone Happy".
He performed the role of Schaunard in the famous 1956 recording of La Boheme conducted by Sir Thomas Beecham.
Reardon was chosen by Igor Stravinsky to sing the role of Nick Shadow on the composer's second recording of his opera The Rake's Progress.