Orpheus is first mentioned in "Hercules and the Tapestry of Fate", where Hercules and Icarus try to get tickets to his concert, only for it to turn out in the end it is cancelled due to a sore throat. He appears on screen in "Hercules and the Prom", where he reveals to Hercules he is tired of not talking and using his voice for money, and later begins traveling, singing concerts for free. His two biggest fans are probably Tempest and the giant Laistrygones, the latter of whom becomes his roadie.
Orpheus doesn't appear in Once Upon a Time. However, he was mentioned by Hades, when escaping from the Underworld with his lover Eurydice, resurrected with ambrosia.