The movie has outraged North Korea for lampooning dictator Kim Jong-Un, giving an early online Christmas present to US viewers.
The madcap, irreverent R-rated comedy was available for rent in the United States from 1800 GMT on several online platforms, a day before a limited release in about 200 cinemas on Christmas Day.
It was being distributed on Google's YouTube for a $5.99 rental fee, on the Google Play app for Android devices and on a dedicated website, seetheinterview.com.
A bawdy, expletive-laden tale full of sexual innuendo and scatological humor, the film's future had been in doubt after Sony said it was canceling the release after an embarrassing cyber-attack on its corporate network and threats against moviegoers.
The US has blamed the hack attack on North Korea, and President Barack Obama has threatened reprisals.
But Sony had come under fire from Obama and free speech advocates for pulling the film, and the studio quickly performed an about-face.
On vacation in Hawaii, Obama, who had previously called Sony's move a mistake, told reporters he was "glad it's being released."
While some US movie theater chains got cold feet after anonymous online threats, a limited number have agreed to show the film from Thursday.
Meanwhile Google and Microsoft joined forces with Sony to release the film to online audiences.
"After discussing all the issues, Sony and Google agreed that we could not sit on the sidelines and allow a handful of people to determine the limits of free speech in another country -- however silly the content might be," Google chief legal officer David Drummond said in a blog post.
Starring comic actors Seth Rogen and James Franco, the film is a silly, low-brow romp about a Central Intelligence Agency (CIA) plot to assassinate Kim.
A kind of a cross between a slapstick James Bond movie and "Hangover," it is aimed squarely at an audience (most likely teen boys) out for a fun but vacuous night at the cinema.
"It has always been Sony's intention to have a national platform on which to release this film," said Sony Entertainment chairman Michael Lynton said in a statement.
"It was essential for our studio to release this movie, especially given the assault upon our business and our employees by those who wanted to stop free speech."
"Merry X-mas MERICA!!!! THE INTERVIEW IS LIVE!!!!!!!!! Watch it," Franco said in a message on his Twitter account.
https://twitter.com/JamesFrancoTV/status/547820465729699840
Rogen apologised to Canadians that it was not yet available for download in his native Canada "BUT will be soon. We are working on it," he promised.
Russell Brand, who shares the same vein of humor, rejoiced on Twitter "saying celebrate freedom and Christmas by watching The Interview."
Celebrate freedom and Christmas by watching The Interview on VOD or in the theatre (do not attempt to assassinate anyone - it's pretend)
— Russell Brand (@rustyrockets) December 24, 2014
"Do not attempt to assassinate anyone -- it's pretend," he added.
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