"Yes it true I'm joining Corrie!!!" she wrote. "As u all know I've been a huge fan for yrs now so can't wait to strut my stuff on those famous cobbles!!"
The former Girls Aloud singer was immediately congratulated by her ex-bandmate Nicola Roberts, who posted: "Amazing! Congratulations babe.. Can't wait to watch <3 xo."
Sarah Harding paid a visit to the Coronation Street set last year
Details of Sarah's role are being kept firmly under wraps, but the blonde beauty will play a "feisty character" who plans to make life difficult for troublemaker Tracy Barlow.
"Sarah is proving to be a gifted and exciting actor and I'm absolutely delighted to have her on board," said producer Stuart Blackburn in a statement. "The viewers are in for a treat as her character will be right at the heart of a massive new story for the Barlows."
Sarah, whose acting credits include Bad Day, Freefall, Run for Your Wife and St Trinians 2: The legend of Fritton's Gold, will appear in four episodes that will air this summer. She will start filming in May.
Sarah Harding previously told HELLO! that she does want "to be a mum one day"
This won't be the first time Sarah has stepped on the famous cobbles. The 33-year-old visited the set for Good Morning Britain last year.
She also said of her cameo role: "I am extremely excited to be joining Coronation Street. As a fan of the show it is a huge honour for me to join the cast. I can't wait to get started!!"
Sarah, who split from her long-term boyfriend Mark Foster last September, has a new man in her life, Jason, who she has known for a couple of years but only started dating.
Sarah Harding has just started dating her new boyfriend Jason
Speaking previously to HELLO! magazine, Sarah admitted that she does see herself having children, especially now that former bandmates Nadine Coyle and Kimberley Walsh are mums.
"It does get harder to see other people have something that you want," said Sarah. "I do feel my biological clock is ticking and while I'm not ready right now, I do want to be a mum one day. I still have a few years to go but I do go through stages where it plays on my mind."