He told NBC News: "He's perfectly positioned as a rising star. I think he'll probably be one of the great ones. His older brother, Chris, could also play him but Liam looks more like an everyman. I think he'd be perfect."
The filmmaker said he has been fascinated by the story of Snowden, who is currently in Moscow and has been on the run since exposing US authorities' data-gathering PRISM programme.
He said: "This is a movie that's playing out before our eyes, even though we can't see anything. We can't see the hero or the villain - the central character.
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Edward Snowden
"Like my last big movie, Salt, it's a story where you're not quite certain if you're dealing with a heroine or a villain. And we may not be certain until the end of the movie or even beyond that. That's a beautiful duality to deal with when you're making a story or watching a movie. You can speculate he's motivated by complete unselfish motives through belief in protecting worldwide public interests. Or you can speculate he was himself a victim of knowing that notoriety might bring him immortality."
Liam, who is engaged to singer Miley Cyrus, can be seen in the second Hunger Games film, Catching Fire, later this year.
Edward Snowden: The Movie
The Elusive Whistleblower: Edward Snowden(01 of12)
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No one knows where he is because he's played by... (credit:Getty Images)
'Hollow Man's' Kevin Bacon(02 of12)
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A handy skill to have when being hunted down by the most powerful security services in the world. (credit:Getty Images)
The Girlfriend: Lindsay Mills(03 of12)
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The heartbroken, pole-dancing, blog-writing poor lass would be played by...
Elizabeth Berkely(04 of12)
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The last time Berkley played a pole dancer in the universally panned 'Showgirls', she was so terrible she'd jump at the chance to redeem herself. (credit:AP)
The Reporter: Glenn Greenwald(05 of12)
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The guy who broke the story would be played by... (credit:CNN/YouTube)
That Guy From The New Adventures Of Superman(06 of12)
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Who mixes the perfect balance of geeky reporter and superhero government-exposer.And has anyone actually seen Greenwald and Snowden in the same room? (credit:December 3rd Productions,)
The Absent Mentor: Julian Assange(07 of12)
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Would be played by... (credit:AP)
Dennis Hurley (08 of12)
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The albino actor would be one of few people able to faithfully recreate the Swede's skin tone after five years indoors. (credit:Dennis Hurley)
The Secretary Of State: John Kerry(09 of12)
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Would be without a shadow of a doubt be played by... (credit:Getty Images)
Sesame Street's Newscaster(10 of12)
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'nuff said. (credit:The Jim Henson Company)
The Big Man: President Obama(11 of12)
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The leader of the 'free' world would be played by... (credit:AP)
Hayden Christensen(12 of12)
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Who played Anakin Skywalker, a character who started out as the hope of the new world only to show his dark side when it was too late to stop him. (credit:Getty Images)