The existing pay-wall, which allows non-subscribers to the magazine web access to editorial published within the past 12 months, free of charge, will now apply to all content more than 90 days old.
In addition, the section of The Economist's website that allows users to browse the current edition of the print magazine is also set to become available to subscribers only.
The move will attempt to reposition the weekly news magazine's content, which prefers to call itself a 'weekly newspaper', as "a premium reading experience" both on and offline.
Remaining sections of the site, including its blogs and audio-visual content, will continue to be free.
Ben Edwards, publisher of The Economist's website, said the brand online had expanded beyond the print issue to become "a hub for intelligent discussion and debate".
He added: "Our intention is to continue to develop intelligent discussion as a free, advertising-supported experience, but to charge for the weekly magazine online."
The Economist is published each Friday in the UK and is available from newsagents and on subscription.
An online subscription to the Economist costs £50 a year, compared to £127 for a print subscription, or £102 if payment is made by direct debit.
According to its own readership figures, the brand attracts more than four million readers globally.
Today's announcement comes as British newspaper and magazine publishers, ravaged by the ongoing advertising recession, continue to publicly debate the pros and cons of charging for some of their content online.
Rupert Murdoch's News International empire, which includes The Times, The Sunday Times, The Sun and News of The World, has made its intentions clear to introduce online subscription services in the near future.
Read how Media Week broke the story here.
