The actresses will play Jenna and Dawn respectively
Jones and Roberts will join the show from 17 June – although Jones has already performed in the show several times as a cover for current Jenna, Katharine McPhee.
Waitress opened at the Adelphi Theatre earlier this year, with WhatsOnStage critic Sarah Crompton saying: "Waitress is a treat… it leaves a pleasantly sweet taste in the mouth."
Sara Bareilles' songs feature in the piece, which is based on the 2007 film by Adrienne Shelly and has a book by Jessie Nelson. The show tells of a waitress and avid baker in a small town working in a diner who is stuck in a toxic relationship.
The show is directed by Diane Paulus, with choreography from Lorin Latarro, lighting from Ken Billington and designs from Scott Pask.
Waitress is currently booking until 19 October. Laura Baldwin, who currently plays Dawn, will return to the role at the end of the summer.