The 31-year-old, who has played Weatherfield's Liam Connor since 2006, reportedly revealed his intention to leave only days before filming his on-screen wedding to Maria Sutherland (Samia Smith).
A source at the soap told the News of the World: "Nobody was expecting this and it's bad news because Liam has become hugely popular with fans. He won 'Sexiest Male' at the British Soap Awards and they had big things planned for him.
"They wanted the Carla-Liam-Maria thing to really step up in pace, with him finally cheating on his girl with his sister-in-law. It would have given them a brilliant storyline which could have bubbled away until Christmas."
They added: "He says that he doesn't want to be typecast."
A spokeswoman confirmed to DS this morning: "We've known for some time that Rob would be leaving at the end of his current contract. It's given the writers time to pen a really good exit storyline for his character, Liam.
"Rob will remain filming with us until around October and he will bow out on screen at the end of the year."
At around the same time last year, Sean Gallagher, who played Rob's on-screen brother Paul Connor, announced his decision to quit the soap after only five months in the role.
Rob will become part of the growing list of characters to leave the soap. The last few months have seen the departures of Liz Dawn (Vera Duckworth), Tina O'Brien (Sarah Louise Platt), Wendi Peters (Cilla Battersby-Brown), Bruce Jones (Les Battersby), Samantha Seager (Jodie Morton) and Zaraah Abrahams (Joanne Jackson).
Julie Hesmondhalgh (Hayley Cropper) has taken a 12-month extended break from the soap but will return at the end of this year, while Julia Haworth (Clare Peacock) is due to go on maternity leave, with her baby due in July.
This month also sees the departure of on and off-screen lovers Rupert Hill (Jamie Baldwin) and Jenny Platt (Violet Wilson).
Bradley Walsh - who played former Underworld boss Danny Baldwin - is still due to return to the Cobbles at some point this year, although nothing has been confirmed.