The 48-year-old actor is reprising his role as Tommy Shelby in an upcoming movie, The Immortal Man, and has been watching old episodes of the drama to prepare.
Peaky Blinders ran for six series between 2013 and 2022.
Murphy said while he found the storylines enjoyable when he was able to detach himself, it wasn't an easy watch because of the scenes involving his late co-star Helen McCrory, who died of cancer in 2021.
"Since I started producing - I was a producer on Peaky - you kind of have to," he told Britain's GQ magazine.
"It kind of takes the curse off of it.
"It was very nice watching it, because it was actually quite a good show."
Asked if he could distance himself from the show, Murphy said "a little bit".
"It was also quite heartbreaking, you know, because I was watching Helen McCrory, and we lost her," he said.
"But you can distance yourself from it, and look at and say, 'right, that's the atmosphere we want, that's the look we need, that's the silhouette, and that's the energy we need from it'.
"We need to turn it up for the movie, obviously."
Despite playing Tommy for so many years, the Oscar-winning star insisted it wasn't "easy" to get back into character but after a few weeks, it was like a "second skin".
"You have to figure it out again," he said.
"It's not easy. You can't just switch him on and off.
"It takes a moment. It takes more than a moment - it takes a few weeks to get back to it.
"I have to watch some of it to remember what it's all about but then when you get into it, it does become like a second skin because I've been playing him for like 12 years or something."
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