Known for its celebrity scoops and topless "page three" models, the tabloid will charge subscribers 2 pounds for a week's access to its website, which will be called Sun+.
Murdoch's British newspaper publisher announced the paywall in March, saying free access to The Sun's online content had become "untenable".
"Asking readers to pay for content is the only way to protect the future of the newspaper industry," said the Sun's new editor David Dinsmore.
"This is a landmark event for The Sun and a testament to the pioneering attitude of Britain's best-selling newspaper."
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The Australian-born media tycoon, 82, placed his British broadsheet The Times behind a paywall in 2010.
The Sun sold around 2.24 million copies a day in June, a Sun spokeswoman told AFP -- compared to 3.12 million copies four years ago.
"Like the other newspapers, there has been a decline in readership in the past years," the spokeswoman said.
The Sun's website, Sun+, currently attracts around 32 million unique users per month, she added.
While The Times' print subscribers get automatic access to its website, The Sun's print subscribers will need to collect 20 codes from their papers in order to access online content for the next month, in a process the spokeswoman admitted was "quite tricky".
Putting The Sun's website behind a paywall is a big gamble for Murdoch, who saw traffic to The Times' site drop off heavily after it began charging for access to online content.
Mike Darcey, CEO of Murdoch's renamed British newspaper wing News UK, insisted last month that the paywall was "working" and that The Times' income from subscriptions was higher than it was in 2010.
A spokeswoman for The Times and its sister newspaper, The Sunday Times, said the two websites currently have some 274,000 subscribers.
The Times' parent company Times Newspapers Limited reported pre-tax losses of 28.7 million pounds (USD 43.6 million) in the year to June 2012.