The actor from The Office plays Dr John Watson in the BBC's re-imagining of the classic character, which begins with him in a war zone in Afghanistan.
"I thought it could go either way. I thought it could be either too anachronistic or a bit too post-modern -- things that I don't really like about television," he says.
"But within a few pages I thought it was brilliantly written. It was a character I could easily see myself playing and wanting to play. It had a real flair and style to it, so I was sold very quickly."
The three telemovies have won wide praise since airing in the UK, with Doctor Who writers Steven Moffat and Mark Gatiss behind them. Freeman's Watson plays alongside a dazzling performance of Sherlock by actor Benedict Cumberbatch.
With writers like Moffat and Gatiss adapting the characters created by author Conan Doyle, it's little wonder such a bold concept took off.
"I know Mark Gatiss too and he's a very clever fellow, so between the two of them they've got Conan Doyle pretty much covered as far as their knowledge of him is concerned. And their taste I trust as well. They're just really, really clever, exciting writers who actors want to work with.
"They give you great stuff to say and great stuff to do, so we're very lucky.
"Sherlock doesn't take any prisoners. It expects you to work as a viewer, which is the kind of telly I like. There's no baby spoon-feeding too much, which I like."
While he admits he read Doyle's original book, Freeman's approach to the role was driven more by the script, but he did research with army personnel to help reflect a shattered survivor of war. When we first meet Watson he is recovering from the trauma of working in Afghanistan.
"I spoke to an army doctor about real experiences about how you would expect to come back from a war situation such as injuries and mental states, all the time acknowledging that we're doing Sherlock Holmes. We're not doing a fact-based hyper-realistic drama.
"I wanted there to be some semblance of respect for the people who are coming back from Afghanistan and Iraq. I didn't want to totally miss the boat, but at the same time you have to know what boat you're in and I'm in the Sherlock Holmes boat. It's not Saving Private Ryan," he says.
"My only job is to play the part that's in the script."
Originally devised as a one-hour drama, the BBC re-worked Sherlock as three 90-minute telemovies. While proving a dynamic crime-busting duo, Sherlock and Watson have won over audiences with the dynamic of their relationship.
Freeman says he relished the opportunity to reinvent Dr Watson.
"I guess what people know about him is that he's bumbling and gasps at everything Sherlock says, so that didn't seem to apply at all for this.
"It was the first time I've read any Conan Doyle. I've seen loads of Sherlock Holmes film and TV characters but I'd never actually read any before. So now I am a bit more familiar with the stories and literature of it, and that's been fun getting to know."
Sherlock airs Sunday and Monday at 8:30pm on Nine.