She wrote the songs. Now she’s going to sing them.

Sara Bareilles is planning to step into the lead role of “Waitress,” the hit Broadway musical for which she composed the music and wrote the lyrics.

Ms. Bareilles, a soulful singer-songwriter, will succeed Jessie Mueller, who has been with the show since it opened last spring. Ms. Mueller’s last performance will be March 26; Ms. Bareilles’s first performance — her Broadway acting debut — will be March 31, and she is planning to spend 10 weeks in the role, through June 11.

“It’s something I’ve been quietly mulling over since the show began,” Ms. Bareilles said.

“So I’m making the big jump, and it feels like a completion of sorts, a coming full circle with this project,” she added. “When I started working on it, I didn’t know how fully it would engulf me and my creative sensibilities. I’m obviously having a hard time saying goodbye.”

Ms. Bareilles’s move, from the world of composing to performing on Broadway, is unusual but not unprecedented. Among the pop stars who appeared in Broadway shows for which they composed music are Sting (“The Last Ship”), Boy George (“Taboo”) and Billy Joe Armstrong (“American Idiot”).