The actress has decided to bow out from her role as fan favourite Becky McDonald after five years in Weatherfield.
Becky is to remain on screen until early 2012 and show bosses have promised that she will feature in dramatic storylines for the remainder of her time on the soap.
The build-up to Becky's exit begins next month when social services start investigating her 'purchase' of nephew Max from half-sister Kylie.
Believing that her arch-nemesis Tracy Barlow (Kate Ford) has reported her to the authorities, Becky soon goes on another rampage - putting Tracy's life in jeopardy and risking the future of her marriage to Steve (Simon Gregson). Details of the dramatic showdown leaked yesterday but the plot has now been officially confirmed.
Further twists and turns are then expected in the coming months as the McDonalds' ongoing story heads towards an explosive exit for Becky.
Speaking of her forthcoming departure, Kelly commented: "It's been one of the hardest decisions of my life. I love Coronation Street and everyone here. I have had the most blissful five years, I wouldn't change one moment of it - but it feels like the time is right to say goodbye to Becky."
Corrie's producer Phil Collinson added: "Katherine is a talented actress who has made the character of Becky a firm favourite with the viewers for the past five years and we will miss her as an actress and a valued member of the Coronation Street family.
"That said, we totally respect her desire to move on and viewers can certainly look forward to an electrifying nine months of gripping storylines involving Becky McDonald as we head towards her departure from Weatherfield."
Today's announcement brings months of speculation surrounding Kelly's future at Coronation Street to an end. Reports first indicated that the actress was planning to leave last December.
> Read our Coronation Street spoilers and news