The 62-year-old, who has played Michael Rodwell on the ITV soap since 2014, said his decision to move on "was a hard one".
The actor said he wanted "freedom to do more projects" and it felt "like the right time" to leave the show.
"The talented team of writers have come up with a very dramatic exit... which will be exciting to film," he said.
Earlier this year Dennis took a sabbatical from the soap to star in a production of Alan Bleasdale's Down the Dock Road at The Royal Court Liverpool.
Michael first appeared on the soap as a burglar who began a relationship with Gail Platt after he broke into her house.
'Fond memories'
His subsequent storylines saw him marry Gail, but split after he discovered she lied to him about the identity of his son. He then began a relationship with Eileen and the Rovers saw many a confrontation between Michael and local builder Pat Phelan.
"As a lifelong fan of the show, playing Michael Rodwell in Coronation Street has been a dream come true. Becoming part of the ITV Coronation Street family has been a wonderful experience and my decision to leave was a hard one," Dennis said.
"I'll treasure the two-and-a-half years I have been part of such an iconic show and move on with very fond memories, so many lovely friends and colleagues and an ambition achieved."
The soap's producer, Kate Oates, said the team was "very sad" to see Dennis leave.
"We have worked on giving him a great story to ensure a fantastic and dramatic end to his time on the Street," she added.
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Les Dennis has announced he is to leave Coronation Street later this year "in a hugely dramatic storyline".