Teasing the Peaky Blinders film, which has been written by the show's creator Steven Knight, Murphy said: "I think it's better to keep it under wraps, keep it a surprise."
Viewers have seen Murphy lead the Shelby organised crime gang with tortured efficiency since 2013 and across six series.
The actor said the length of time he has played Shelby has been "defining" for him.
"To grow older with a character, you don't really get to do that, and that is the joy of long-form television," he said.
"We never anticipated that the TV show would have that impact, would be so adored and have that longevity. It is defining."
Since the original series concluded in 2022, Murphy has also starred in Small Things Like These and won an Oscar for his leading role in Christopher Nolan's Oppenheimer.
Discussing the key to Peaky Blinders' success, Murphy said it is a sort of "magic". "Mostly the writing, I think, but also it was a moment in time."
He added: "The beauty of that show is that I have gone off and done other things in the meantime and played lots of other characters."

