Law to play Dr Watson
Robert Downey Jr has signed up to play the famous detective, with Rachel McAdams, Mark Strong and Kelly Reilly also attached to the project.
Based on the original stories by Arthur Conan Doyle, Ritchie said he intends to make a modernised version of the tale.
"I'd like to bring something new to this project - I have a few tricks up my sleeve. It won't be a traditional Guy Ritchie thing, it will be a new Guy Ritchie thing," he said.
Iron Man star Downey Jr was introduced to the project by his wife Susan, who works for the film's producer Joel Silver.
"I think me and Guy are well-suited to working together," Downey Jr said.
The movie is scheduled for release in October next year and will rival a comedy-based Holmes film starring Sacha Baron Cohen.
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