Digital Spy and other journalists caught up with Benedict to discuss his role in the five-part period drama, based on Ford Madox Ford's novels, and got the scoop on his new stardom and his Hollywood experience.
Was it the chance to work with Tom Stoppard that attracted you to Parade's End?
"Yeah, because his output's slowed a little bit in recent years, so yeah, it was a huge pull. I didn't know the books, but I knew of Ford Madox Ford because of [1915 novel] The Good Soldier but then I started reading the books and that really drew me in.
"I completely fell in love with Christopher Tietjens, the most adorable and long-suffering but virtuous character I think I've ever played. I really think he has many admirable qualities I'd like to siphon off into my life.
"Tom was obviously a massive pull, but also Rebecca Hall, who I've worked with before, but not opposite on such a large scale. And then [director] Susanna White as well, and the fact that it's HBO.
"Also, I do have a fascination with that era. It's a very interesting part of English history and something we all seem to be slightly obsessed with now - there's Birdsong and Downton and now this.
"We're living 100 years from where it actually began. No survivors can give us any evidence, nor will history other than what's been recorded. So storytellers like to re-examine an era where there's nobody alive to tell those stories anymore. People can't tell us a story in an interview, so it's quite nice to revisit it through a fictitious or dramatised account of reality.
"It's 100 years on, yet I think there are a lot of similarities with today. Europe is falling apart. Parade's End is about the death throes of aristocracy as told through the prism of this love triangle over the duration of the First World War. The war itself is of constant fascination to us, but it's part of the series rather than the whole reason to it. It's not like Birdsong, which is very much a war romance. I just think it's important to look at an era that's beyond our living experience."
There were reports that you had criticised Downton Abbey...
"Yes, I was sort of quoted in the press out of context. All these people [from that show] laughed when they read it. I thought the second series sort of dropped off a bit at the end, but it's still a great show that keeps you hooked. What we're doing is not supposed to be compared to that."
How would you describe the love triangle between the characters in Parade's End?
"Sylvia (Rebecca Hall) is kind of the modern woman. It's a terrible mismatch - Christopher sees her as damaged goods and is trying to do right by her and be kind and understanding of her appalling treatment of him, but really he's kind of exacerbating it and killing her with his kindness. What she wants is to be treated sternly, and they're always out of sync. That's the tragedy of it.
"And then Valentine (Adelaide Clemens) comes along in his life, who's younger than him but has this incredible old soul, and has this incredible command of language. She can challenge him. She's beautiful and promises something in the future for him. She's exciting but forbidden fruit."
Christopher is described as bulky in the novel, which clearly you're not...
"Yeah, that's what I said to Tom and everyone, 'Why do you want me to play this part so badly?' Obviously it's an economical thing about bringing an audience from Sherlock, that was obviously part of it. But Christopher is a fat blonde Yorkshireman - I didn't get it. I keep on looking at myself getting angry at the fact that I'm not fat enough! I had to eat myself into the role."
Has shooting in Hollywood for Star Trek and other films changed things for you?
"Oh yeah. Everything kind of scales up. Your hours are more weird... you're working harder to an extent. Star Trek was an action movie as well as a drama, so it involved a lot of training and I put weight on - I went up four suit sizes at one point.
"It was hard work, but you're paid to scale. The money with films is what directors get to play with, that's what you really notice. [As an actor] you can get paid more for doing TV work than you can for films.
"I could have made much more money if I'd stuck around doing plays than if I was in Star Trek. But you just get to play with bigger toys that no other schedule or budget would allow in a TV structure."
You seem to be on a career high - are you ever worried that it might come to an end?
"No, I don't think so. It hopefully won't. Maybe this drama will be the death knell. People will go, 'Is this really what Sherlock should be doing next?'
"But I'm very proud of it. I treat each job as a new experience. I'm not nervous of the work drying up. It's been great to have back-to-back, well-received work."
Do people treat you differently after the success of Sherlock?
"Yeah definitely. What's quite nice is that they're by and large an intelligent breed, so they've gone over my back catalogue and got why I've done what I've done and how I've done it. Many more of them have seen [2005 BBC mini-series] To the Ends of the Earth then would have watched it originally, so that's nice."
Is it strange becoming a recognisable face?
"Oh yeah, yeah. There's some worrying behaviour. I worry for them, not for me. Any privacy in public is a hard thing to negotiate. The only thing that really pisses me off is people trying to surreptitiously take a photo of me with their phones. That really f**ks me off.
"It's not just that I feel it's invasive - it's cowardly and pathetic. Just ask me if you really want a photograph. People's response is 'I'm a bit shy' - well then don't f**king take a photograph!"
Can you tell us about your experience on The Hobbit movies?
"I'm not really allowed to talk about it. But it was great, I had a very isolated time with Peter Jackson and Fran Walsh."
Is it technically the most challenging thing you've ever done?
"No, I don't think so. It's very freeing once you put the suit on, and you have to be free. Andy [Serkis] for all his brilliant work is playing a primate, something relatable to us. Whereas a serpent with cold blood who's twice the size of the Empire State Building who lives in a mountain is harder to do that with! You have to lose your s**t on a carpeted floor and imagine yourself into it."
Why do you think you've previously been cast in a lot of period dramas?
"I haven't done period dramas back-to-back, or really anything back-to-back. You get asked to do what you're most recently famed for, so I'm careful of not repeating myself. But I've got a long face... I look a bit weird... I suit period costumes, I guess!"
Parade's End begins on Friday (August 24) at 9pm on BBC Two.