Tevis met Morricone while living in Italy in the 1960s, and suggested working together. A 1962 recording of the song "Pastures of Plenty" by Woody Guthrie became a small hit single (RCA PM45-3115). Morricone later reworked it into the title theme of the famous Spaghetti Western movie "A Fistful of Dollars" directed by Sergio Leone and starring Clint Eastwood (without Tevis lyrics). Later they continued to collaborate on a number of recordings. Tevis is credited with singing the lyrics of songs on the soundtracks of several Spaghetti Western movies, including:
"A Gringo Like Me" from the film Gunfight at Red Sands
"Lonesome Billy" from the film Guns Don't Argue
"Per un Pugno di Dollari" (A Fistful of Dollars)
Since the 1970s Tevis also produced audio recordings designed to train different families of songbirds to talk.
In his last years he suffered from Parkinson's Disease and had almost lost his voice.