The trio will join 12 other celebrities on the 2017 series, which launches on BBC One next month.
McGee is best known as the widow of magician Paul Daniels, while Burke won 2008's X Factor and is a West End star.
Peacock has won two Paralympics sprinting gold medals and is the first celebrity hopeful to have a disability.
His appearance follows that of former Royal Marine and fellow amputee Cassidy Little, who took part in a "people's" edition of Strictly in 2015 as well as that year's Christmas show.
The new series of Strictly will begin with a launch show on BBC One on 9 September. Tess Daly and Claudia Winkleman will return to host the first series not to have Len Goodman as a judge.
Bruno Tonioli, Darcey Bussell and Craig Revel Horwood will instead be joined by international ballroom champion Shirley Ballas.
Here is a complete rundown of the contestants for the show's 15th series:
Debbie McGee found fame at the side of Paul Daniels on his TV magic show in the 1980s and went on to marry him.
Her Strictly appearance comes seven years after her late husband took to the dancefloor on the show's 2010 edition. He died last year.
Speaking of her own impending appearance, she said: "The excitement is overwhelming. I can't stop smiling. It's been the hardest secret I have ever had to keep!"
Jonnie Peacock has won gold in the T44 100m at two Paralympics, two World Para Athletics Championships and two European Championships. But can he win the Strictly glitterball?
The 24-year-old had his right leg amputated below the knee after contracting meningitis as a child.
"The opportunity to be the first contestant with a disability to take part in Strictly's main show was too good to turn down," he said.
"I've got no previous dance history outside of the occasional 'worm' at a mate's party and I know this will be a challenge and a new experience.
"I can't wait to see what I can achieve and how far I can push myself."
Alexandra Burke took The X Factor by storm in 2008, with her winner's single Hallelujah selling more than a million copies.
Since then, she's established herself on stage in such musicals as The Bodyguard and Sister Act.
"I love this show and have followed it from the beginning, so being able to be a part of it is just a dream come true for me," she said.
"I am very nervous as I am a singer not a dancer, but I am going to give this my absolute everything."
Chizzy Akudolu left Holby City in June after five years. Before that, she had roles in The Inbetweeners, EastEnders, Silent Witness, Hollyoaks and Twenty Twelve.
Viewers have already seen her strut her stuff in BBC One's Let's Sing and Dance for Comic Relief. She appeared with two Casualty stars earlier this year, finishing second with a routine set to Bruno Mars' Uptown Funk.
She said: "When I was 13, I made the finals of a disco dancing competition once but there was this amazing girl who exploded onto the stage with a gorgeous sequined costume, throwing glitter everywhere.
"I knew it was game over for me. That was then, this is now and this is my chance to have even more sequins!"
Charlotte Hawkins's broadcasting career has included stints reporting on LBC, Sky News and Channel 5.
But she currently reads the news on Good Morning Britain, which airs weekdays on ITV.
"I did dancing as a child, a bit of ballet, and I do a bit of dancing round the kitchen with my two-year old but I don't know if that counts," Hawkins joked on Monday's programme as she announced she'd be doing Strictly.
She added: "Thank you for all the support. This is setting me on the way now. The excitement's really beginning. It doesn't feel like it's really happening until people know."
Comedian, actor and TV presenter Brian Conley joined the line-up on Friday.
His 40-year career in showbiz has included presenting the Royal Variety Performance eight times and fronting his own hugely popular entertainment show on ITV.
"My family all love the show and can't wait to see me do my Dad dancing on national television," he said.
"I know it's going to be a lot of hard work but I'm up for the challenge, so bring on the spray tan and sequins."
Susan Calman's TV credits include BBC One daytime quiz The Boss and kids' quiz Top Class.
She's also made an appearance on numerous TV panel shows and starred in Sharon Horgan and Holly Walsh's BBC Three sitcom Dead Boss.
The Scottish comic told the Jeremy Vine show: "I am the last person on the dancefloor!"
"I haven't worn heels or a dress since the 1970s... my mother will die happy to see me in a dress and glitter."
Aston Merrygold was a member of boyband JLS, who came second in the 2008 series of X Factor.
The band went on to huge chart success but split up in 2013, after which Aston went on to become a judge on Sky 1's Got to Dance. Earlier this year, he released his first EP as a solo artist.
"I'm both nervous and excited to learn from the professionals about a whole new way of dancing!" he said as he was revealed as the latest contestant during the Scott Mills show - he's the 200th participant in Strictly's history.
Chef Simon Rimmer revealed he will be a Strictly contestant during his Sunday morning Channel 4 show, Sunday Brunch, which he co-hosts with Tim Lovejoy.
He said he had "never danced in my life", and joked that he had lost all co-ordination between the top half and bottom half of his body since becoming a father.
Rimmer said: "I am so excited, terrified and proud to be invited... Nobody will try harder, have more fun or get more out of it than me. I can't wait."
The 54-year-old has also appeared on the BBC's Great British Menu. The food writer also owns nine restaurants.
Scottish actor Joe McFadden is probably best known for playing the role of Raf di Lucca in Holby City.
His first TV role was in the STV soap Take The High Road before starring in The Crow Road, based on the book by Iain Banks.
He major breakthrough came when he played PC Joe Mason in Heartbeat for two series.
He has also taken on theatre work in stage productions as diverse as Chitty Chitty Bang Bang, Rent and Rainbow Kiss.
Writer and broadcaster The Reverend Richard Coles is the only UK vicar to have had a chart-topping single - and now he's the first one to star on Strictly.
He told BBC Radio 2's Chris Evans Breakfast Show: "A major dance talent was waiting to be discovered. I just wonder what took them so long. I'm in it to wing it, as they say."
Coles, who had hits with Jimmy Somerville in The Communards including Don't Leave Me This Way, said he had a "comprehensive briefing" from former Strictly star Ed Balls as part of his preparations for the show - and has also "cut down on pork pies".
But he said he might not be able to take part in the Strictly live tour, as it clashes with Epiphany.
He hosts BBC Radio 4's Saturday Live and is a contributor to Pause for Thought on Chris Evans' show - as well as being vicar of St Mary's Church in Finedon, Northamptonshire.
Actress and former glamour model Gemma Atkinson currently co-hosts Manchester radio station Key 103's breakfast show - which she will continue to present during Strictly training.
Her TV credits include roles in Casualty, Emmerdale and Hollyoaks.
"I'm beyond excited and incredibly nervous, but looking forward to learning a new skill," she said of joining this year's Strictly.
TV presenter Ruth Langsford is often seen hosting This Morning (when Phil and Holly are away) alongside her husband Eamonn Holmes.
Ruth said: "The sum of my dance experience is throwing a few shapes at a party, I've never had a dance lesson in my life."
"Without doubt, [Strictly] will be the scariest yet most exciting thing I've ever done."
EastEnders actor Davood Ghadami, who has played Kush Kazemi in the soap since 2014, said it was "such an honour" to be joining the dancing show.
"It's going to be exciting, challenging and terrifying all at once and I am so looking forward to stepping out of my comfort zone and learning to dance," he added.
Mollie King was the first contestant to be unveiled for this year's series.
The Saturdays singer told Radio 1's Nick Grimshaw (above) she was "so excited" and always watched the show with her family, adding that she "can't wait to get into the sequins".
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TV personality Debbie McGee, singer Alexandra Burke and Paralympian Jonnie Peacock are the final contestants to be announced for Strictly Come Dancing.