Formerly best known as one half of comedy theatre company Plested And Brown (with Clare Plested), and a past regular on the Edinburgh Fringe with acclaimed shows such as Flamingo Flamingo and Hot Pursuit, Brown's life was transformed by a call from his agent urging him to audition for The Hobbit.
His response was immediate: "I was like, 'I absolutely can't do it. I'm in the middle of a pantomime. I've got a lot of commitments...' But he said, 'this is not a touring version of The Hobbit! You're not going around village halls or provincial theatres. This is Peter Jackson's Hobbit'!"
Even then, Brown, 32 (pictured), wasn't expecting much, given that he was asked to read for the role of Bilbo Baggins. But he went along for the experience. "I'd read the book but couldn't remember it that well. But I knew I wasn't really a Bilbo type."
A day later, after his audition had been uploaded and sent to Peter Jackson and screenwriter Fran Walsh in New Zealand, he got the call.
"I got a call-back saying, 'They've fallen in love with you. You're not Bilbo, which I knew already, but they're thinking of a dwarf'."
The dwarf in question was Ori, one of the 12 companions of Bilbo and Thorin, and brother to Dori and Nori. But even then, Adam had to wait eight or nine weeks to hear anything more.
"Suddenly, I got a phone call and it was a case of being told to get ready to fly out next month to New Zealand on what was, then, a two-movie deal. I would be living in Wellington. These were my fellow cast-mates. And I'd be sorted out with a house and a car out there. It blew my world upside down. It's a weird thing to take in. It's the most exciting thing, but so daunting.
"It almost became too much at times and it was so emotional. I mean, I've had more call-backs for commercials. I had to ask, 'Surely I need to meet Peter Jackson and Fran?' But they insisted and the next thing I knew I was flying first-class with Martin Freeman on a Quantas plane to New Zealand and then having a barbecue with Peter and his team and being welcomed to Middle Earth!"
Since then, life for the Hungerford-based actor has been something of a fantasy. He's got to meet and share cucumber sandwiches with Sir Ian McKellen, lived next door to Freeman and Orlando Bloom and learned how to act against CGI monsters and green screen.
One of his fondest memories, though, was stepping onto set, in costume, on that first day. "Peter knew it was my first time and turned to the set and said, 'This is Adam's first time on a film set'. And everyone gave me a round of applause. Peter then said to me, 'Don't worry about a thing. We'll start you off very slowly'."
Getting into character also proved fun, even if perfecting Ori's look proved painstaking. "I think we went through four or five different noses for Ori," he says.
So, what is it like referring to his cast-mates as new friends? "That's surreal. You've previously just watched these people on TV or seen them in theatre and now I'm going around their house for dinner and stuff. It's madness [when you're] out there, but what's even more strange is coming back to London and having Sunday roast with Sir Ian!"
And what about meeting someone like Cate Blanchett? "It's funny... there were practically no females on the set. It was such a heavily male cast that as soon as she started working we were like bees around a honey-pot," he laughs.
Perhaps the most mind-blowing aspect of the whole thing, however, is just how much Brown features in the film and the possible impact it will have upon his career.
"I've had a friend call me [recently] and say, 'I'm in Times Square and I'm looking at your face on a billboard'. It's mental. I've always kind of said to myself that Ori isn't really a big part of all this. He supports Bilbo and Thorin's story, so if I'm lucky I'll get a few scenes. But it really does look as if the dwarves will be the emphasis of all three movies. And that's great because that's what the books are about."
So, what's next for Brown? Will he continue to make more movies and will he ever come back to Edinburgh?
"I think with Plested And Brown we have made a conscious decision to take a break. We'll write some stuff because we're both really keen on writing but I think we both want to write some films now. I certainly do, based around my experiences of the film world so far. I've definitely got a taste for it now."
The Hobbit: An Unexpected Journey opens in cinemas on Thursday, December 13.