In 1997, Ms. Chenoweth had her Broadway debut in “Steel Pier,” playing Precious McGuire, an ambitious young newlywed in a dance marathon. She might as well have been Mildred Plotka, for all the director, Scott Ellis, knew at the time.

“No one knew who she was,” Mr. Ellis said. “She came in and started singing. When she left, we were just like, ‘Who the hell was that?’ She was this petite girl who came in with this voice, and it was dumbfounding.”

That was then. A Tony Award for “You’re a Good Man, Charlie Brown” came soon after. And now Ms. Chenoweth has become one of the rare Broadway stars crossing over into the wider pop culture. If you didn’t see her playing Glinda onstage in “Wicked,” perhaps you saw her on television, in “The West Wing” a while back or, more recently, as a boozy sexpot in “Glee.” Or maybe you heard one of her recordings or went to one of her concerts or caught her at the movies playing Jennifer Lopez’s friend in “The Boy Next Door.”

For a time, rumor had it that she would return to Broadway in the title role of “Hello, Dolly!” Instead, it’ll be “On the Twentieth Century,” a big, brassy, old-school 1978 musical about show business (what better subject for show-business people?) Cy Coleman wrote the music; the book and lyrics are by Betty Comden and Adolph Green.

For Ms. Chenoweth, the project had a sort of eerie inevitability — and not just because her Maltese is named Madeline Kahn, after one of Ms. Chenoweth’s heroines, who was Broadway’s original Lily Garland.

She first heard about “On the Twentieth Century” back in Oklahoma. “My voice teacher, Florence Birdwell, said, ‘There’s a show that I think one day you will do,’ ” Ms. Chenoweth said. “I said, ‘O.K., whatever.’ ”

Much later, she got a record deal. One of the songs on the album was “If You Hadn’t, But You Did,” lyrics by Ms. Comden and Mr. Green. Ms. Chenoweth invited the pair to the recording.