The as-yet-unnamed web-TV service will launch in the first half of 2012 and provide instant access to a range of Sky content, including hundreds of films from Sky Movies.
It will be available to anyone in the UK on any connected devices, regardless of whether they take the Sky Broadband service.
Sky said that the new service "will be an additional choice for people who don't currently subscribe to a pay TV service".
It will also compete with Netflix, the US subscription streaming giant which launched in the UK and Ireland this month, along with Amazon's LoveFilm.
At launch, the web-TV service will offer access to a range of Sky content, including Sky Movies, while sports and entertainment will follow soon afterwards.
Aimed primarily at people who have so far declined to take up a TV service from Sky or Virgin Media, the web TV service is part of Sky's attempt to further monetise its range of expensively-acquired content.
The web-TV service will have no minimum contract, as customers can choose from a variety of payment options, including monthly unlimited streaming of Sky Movies, or just specific pay-per-view access of certain titles.
Sky said that the new service will be offered over a range of devices, including connected TVs, laptops, Macs, smartphones, tablets and games consoles.
More details will be supplied closer to launch.
Sky previously offered an online TV service called Sky Player, but that was rolled into the new Sky Go multi-platform TV service when it launched last year.
Alongside the new web-TV service, Sky Go will remain a "bonus service" for existing Sky TV customers, offering access to live channels and on-demand content.
The part-Rupert Murdoch-owned satellite TV giant said that the "launch of a new internet TV service will complement Sky's existing pay-TV services and open up a wider opportunity to bring its content to more consumers".
"This exciting new service will offer some of Sky's most popular content through a wide range of broadband connected devices," said Jeremy Darroch, the chief executive of Sky.
"Alongside the continued growth of our satellite platform, this will be a new way for us to reach out to consumers who love great content, but may not want the full Sky service. Bringing a distinctive, new choice to the marketplace will help us meet the needs and demands of an ever wider range of consumers.
"This new product launch will build on our early leadership in multi-platform distribution. It will allow us to make our expertise and investment in content and technology work even harder, extending our options for continued growth."
Yesterday, Sky made a significant step towards broadening its TV-based video on-demand offering by agreeing deals to make BBC iPlayer and ITV Player available to around 5m of its satellite TV homes.
> Sky partners with Zeebox social TV service