The 46-year-old joins actor Will Mellor on the line-up, which is being unveiled across the next few days.
Kym found fame in the band Hear’Say, who were created through ITV show Popstars in 2001, before turning to acting and starring as Michelle Connor in Coronation Street.
Driver flees and passenger injured as car crashes into Wigan house
Flames engulf two cars and spread to Wigan house as fire breaks out in early hours
Wigan family seeks legal action after being struck down with gastric illness while on holiday in Turkey
Wigan man jailed for obstructing railway and causing £9k of delays
Wigan man due in court accused of raping woman three years ago
She now co-presents Morning Live alongside Gethin Jones and recently appeared in the touring theatre production of Fatal Attraction.
Speaking to BBC Breakfast via video call from holiday, she said: “I am really looking forward to it. I am nervous – but I am really looking forward to it.”
Kym said her previous experience in dance would be unlikely to help her on the show.
She said: “I am just very keen to learn. Watching it, I have done dancing before when I was a little girl and in Hear’Say but it was a very different style of dance.”
She said her husband, army major Scott Ratcliff, was “extremely excited” about her being about to teach him how to dance properly for mess balls.
Marsh was joined on screen by her parents Dave and Pauline, who she was on holiday with, with her mother saying she was a long-standing fan of the show.
Questioned over how she will react to being grilled by the judges, Kym said: “Listen, I was judged by Nasty Nigel (Nigel Lythgoe) on Pop Stars. Don’t forget that. He was the villain back in the day.
“I think I will be fine with it. These are people who I truly respect because this is what they do. I will have to suck it up, I guess. I will be fine. I won’t start waving my fist at people or anything like that.”
It will be the 20th series of the show and audiences will return to the studio this year, with the launch show scheduled to be recorded on September 7.
Four new professional dancers will appear in the next series of Strictly, creating the show’s largest ever roster.
The last series of Strictly was won by Rose Ayling-Ellis with her professional partner Giovanni Pernice.