The pair will share the role of Betty on the tour
Sam Bailey and Elaine C Smith will join the previously announced Jodie Prenger for the UK tour of the new Fat Friends musical.
Former prison officer Bailey is best known for winning the 2013 series of The X Factor, and appeared in the 2016 touring production of Chicago as Mama Morton. She will share the role of Betty with Smith.
Smith is best known for her roles in Two Doors Down and Rab C Nesbitt, and will play the role of Betty during three Scottish dates in Edinburgh, Glasgow and Aberdeen. Her stage credits include touring productions of Annie, Calendar Girls and the Susan Boyle musical I Dreamed a Dream.
As previously announced Prenger will play Kelly Stevenson when the show opens in Leeds in November.
Based on the '00s ITV sitcom, the musical follows a slimming club in Leeds and will see the characters put through modern weight loss techniques like Zumba.
Directed and written by the show's original creator Kay Mellor, the show will have music by Nicholas Lloyd Webber and designs by Bretta Gerecke.
Fat Friends The Musical will run at Leeds Grand Theatre from 7 November until 2 December before embarking on a UK tour.