The series - written by Bodies creator Jed Mercurio - deals with police corruption and also stars Lennie James (The Walking Dead) and Vicky McClure (This Is England).
Digital Spy caught up with Martin - who plays moralistic copper Steve Arnott - a few months back, while shooting on Line of Duty was still ongoing, to get all the scoop on the show...
What is Line of Duty all about?
"Basically it's a cop drama. It's about an anti-terrorist copper called Steve Arnott who I play. After an operation goes wrong, he's removed from active duty, pending the inquest, and during that time he's moved to anti-corruption, which is basically investigating other police.
"From talking to some police, they're not the most popular people among police themselves, so he's not too happy about it to start with. But from starting to work with some of the people, he kind of understands that there are some bent coppers, and he goes after them."
What can you reveal about Steve? Is he a trustworthy character?
"Yeah he is, he's sort of the moral compass of the piece in some ways. He's very invested in the truth of things and he believes in his job. He's kind of relentless when he's got his mind on something, he tends to chase things down. He's a lot of fun to play."
Was it a change of pace for you, playing a cop?
"Yeah, it's probably in some ways a bit more grown-up for me. TV is so different from film - it's so quick and even on something with a decent budget like this, it's just a completely different world from film, so it takes a day or two just to get back into the swing of it.
"But it keeps you really sharp as an actor - there's no messing about. You realise how spoiled you get on film sets, because you have time to do take after take. Don't get me wrong, we're not rushed on this whatsoever but you have to be on the ball. And because I'm doing another accent at the same time, I just need to be properly focused."
Did you struggle with the English accent?
"The thing is, as you can probably hear at the moment, my accent is pretty strong. But I'm lucky, I've got two really nice voice coaches that I've worked with over the years and they sort of gave me a grounding. It's just part of the job."
Line of Duty has a terrific cast - what's it been like working with your co-stars?
"Amazing. Because we're all based in Birmingham together, we became a very close group very quickly. As you said, it is an amazing cast and I'm very chuffed to be involved in it. We all just got on really well together and we worked well together. So hopefully it's going to be something pretty good."
There are a lot of cop dramas on TV - what makes Line of Duty stand out?
"Well, from the little bits I've seen, it's shot incredibly well, it looks really cool. Also, I think at the moment - obviously with the incident that sparked the [London] riots and alleged police collusion and the phone hacking stuff - the time couldn't be better for this sort of drama, looking at police corruption.
"I don't think we could have bought that publicity - it seems like the right time for something like this to come about."
Since the show deals with themes of police corruption, do you think it could prove controversial?
"Of course, but again, it's TV. Hopefully we are approaching some issues that do have to be looked at, but at the same time it's a drama, a fictional drama. But the scripts are great and that's always the basis for a good show. Basically, in some ways, our job is just not to mess it up! It's all there on the page, so we just need to make the most of it."
Were you a fan of Jed Mercurio and his previous work - shows like Bodies?
"I don't watch a lot of TV to be honest, but I'd heard great things about Bodies and Jed's style of writing. People were telling me how good his previous stuff was. Jed is an ex-pilot, an ex-doctor - he's a talented, talented guy!"
You've done some TV work in the past but recently you've focused more on film roles, so what was it that lured you back to television?
"Definitely the scripts, and it was a change of pace for me, something maybe a bit more wide-ranging. Again, the cast was incredible - when I heard who was involved, I knew it was a great opportunity for me."
Did you take all your inspiration from the script or did you do any research into corruption and being a cop?
"Not tons, because I was on another job when I got cast. But Jed is so thorough, so anything you need to know, you just go to Jed - he's sort of the go-to guy for everything.
"And again, everything's really on the page - you just play it. There's tiny bits [of research} I did here and there but there's alleged corruption all over the place on the news and stuff so you just sort of keep your ears open."
Do you think Line of Duty could continue into a second series - do you see it as something long-running?
"Long-running, I'm not sure, but maybe, yeah, I think [a second series is] the idea. But it needs to come out and do well first before we start thinking of anything else.
"Maybe that's the idea but I'm a great believer in getting my head down and putting out a great show to start with, or a great film or whatever. Until it's done and dusted I don't like to jinx things."
If you had to pitch Line of Duty to an audience, why should people tune in?
"Because it's amazing. The scripts are great and the cast is incredible, so hopefully when we're done we've got something pretty special."
Line of Duty begins on Tuesday, June 26 at 9pm on BBC Two.