The broadcaster, 45, confirmed the good news via Twitter on Saturday (15 August).
BBC Proms presenter Katie said: "Well hello you lovely #strictly fans! I've got the lights & dance floor, now all I need are some moves..."
Describing her happiness at being a part of the BBC dancing show, she added: "I'm extremely excited to be part of such a wonderful show. Strictly Come Dancing is a national treasure."
She also joked: "My dancing daughters have been trying to show me all their stretching exercises.. but they are way out of my league. [I'm a] typical wedding dancer... Two glasses of Prosecco and I'm truly fabulous. Or so I think."
Katie lives in Sussex with her husband John Vincent and daughters Natasha, 15, and Eleanor, 10.
She once admitted she was "slightly obsessed" with the BBC's popular dance show, which is hosted by Tess Daly and Claudia Winkleman.
Former ITV news reader Katie joins BBC presenter Jeremy Vine, celebrity chef Ainsley Harriott, former Coronation Street star Georgia May Foote and Eastenders actress Kellie Bright, who are all confirmed contestants.
The 13th series of Strictly kicks off on BBC1 in September.
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