Tarmey, 69, plays Jack Duckworth on the long-running series.
The BBC said the actor's decision to leave the ITV show follows the 2008 departure of actress Liz Dawn, who played his wife, Vera.
"People often ask me if I like Jack Duckworth and I always reply: 'Like him? I bloody love him!,'" the BBC quoted Tarmey as saying. "Because of him I have made some fantastic friends and traveled all over the world and I will be sorry to say goodbye to Jack. ... I had originally wanted to retire last year but producer Kim Crowther and my wife Ally persuaded me to stay for the show's 50th anniversary, and I am glad that I made that decision. I have had some great story lines over the past three decades and I am looking forward to seeing what Jack's final story will be."
An ITV spokesman told the BBC the plot surrounding Tarmey's exit is still being worked out.