The singer made the announcement during an appearance with her bandmates on BBC Breakfast, reported Digital Spy.
"I'm such a huge fan of Strictly! I've always wanted to be a part of the show - it looks like so much fun and the costumes are just gorgeous," said Frankie.
"Like so many little girls, I used to take dance lessons when I was in primary school and I really love dancing but this is going to be so different from anything I have done with The Saturdays. I just can't wait to get started," she added.
She married her long-term partner, former footballer Wayne Bridge, in June. The couple have one child together, a boy named Parker.
Before joining The Saturdays, Frankie - then known as Frankie Sandford - was a member of S Club Juniors, scoring six top ten hits.
The Saturdays have had four top ten albums and 13 top ten singles and this week released their singles compilation Finest Selection, including new single 'What Are You Waiting For'.