The classic BBC comedy is returning for three special episodes over the festive period.
McCartney and Bunton have now revealed that they have cameos in the series alongside Olympic athlete Dame Kelly Holmes, The Daily Telegraph reports.
McCartney will appear when Edina (Jennifer Saunders) and Patsy (Joanna Lumley) visit her shop, while Bunton will play a friend of Edina's daughter Saffy (Julia Sawalha).
"It was wonderful to be a part of," Bunton admitted. "All my friends are so jealous."
Meanwhile, McCartney said: "It's not exactly my idea of fun, but it's Ab Fab, and how can you say no to Ab Fab? I'm sure I'll be terrifying, but you know."
The Killing star Sofie Gråbøl has previously confirmed that she has a cameo in an episode of Absolutely Fabulous.
The show will return at 10pm on Christmas Day on BBC One.