The Harry Potter star, who has been cast as an angel in a new US television series, also said he knew friends for whom faith has "really helped them".
Radcliffe, 29, told the New York Post: "I don't expect there to be a God and an afterlife - I would be pleasantly surprised if there was."
"There was a time when I was in my teens when I was kind of irritatingly belligerent about atheism. And I'm just not anymore.
"I'm fully aware that religion is a huge part of a lot of people's lives.
"Everyone can believe whatever they want, as long as it's not hurting anyone and as long as you don't think that gives you the right to tell someone else how they can live their life."
The actor was speaking ahead of the US premiere of Miracle Workers, a comedy set in a version of heaven where God decides to destroy the earth. Radcliffe's character, Craig (a junior angel) is tasked with intervening.
Premier reported on an interview where Harry Potter author JK Rowling said Christianity "inspired" the book series - which received a mixed reaction among believers.
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