The Him & Her actor will play Henry Knight in 'The Hounds of Baskerville', the second episode of the detective drama's 2012 run.
"It's amazing to be a part of it," he told Cult Box. "I think a lot of people are anticipating it because it's one of the most well-known of Sir Arthur Conan Doyle's stories, so there's quite a lot of pressure on it and hopefully it delivers the goods!"
Tovey added that Conan Doyle's original 1902 novel has been given "a completely modern twist" by writer Mark Gatiss.
"The beauty of Sherlock is that it's completely loyal to the style and tone of the books, but there's this juxtaposition of old and new," he said. "What is so exiting about the show is that balance and the quirky reinterpretation of it all."
Spooks star Lara Pulver will also appear in the second series of Sherlock as Irene Adler.
Earlier this month, the actress told Digital Spy that Sherlock (Benedict Cumberbatch) will have an "infatuation" with her character.
"We're both very much playing a mind game with each other," she revealed. "We've met our matches with each other."
Sherlock will return to BBC One in early 2012.
Watch Lara Pulver discuss her Sherlock role below: