Channel 4's Ugly Betty is one of the shows likely to be on the service
The service is set to go live in 2008 and will offer viewers access to current shows and archive material.
Plans will have to be approved by the BBC Trust and the other broadcasters' boards, and a name for the service will be unveiled ahead of its launch.
The three broadcasters currently offer their own separate on-demand services.
The BBC's iPlayer and ITV's catch-up service will continue to exist along the new online "aggregator", which will provide a complement to the established providers.
However, Channel 4's 4oD will no longer be a standalone service once it is incorporated within the project.
Programming from all three broadcasters will be available for free download, streaming, rental and purchase via the internet, with expansion on to other platforms planned.
John Smith, the chief executive of BBC Worldwide, said the venture was a "historic partnership" between the BBC, ITV and Channel 4.
"The new service will contain some of the very best of the UK's content for consumers to view in one place, which will be both easy to use and great fun," he added.
Michael Grade, ITV's executive chairman, described the project as having the potential to become "an important shop window for UK broadcaster content and a great destination for viewers".
For Channel 4, chief executive Andy Duncan said further innovation in the area of on-demand would "give viewers ultimate control over what they watch and when they watch it".
"Partnering and sharing expertise is the best way of doing this," he added.
The BBC and ITV's on-demand services launched earlier this year, with the commerical broadcaster initially concentrating on soap opera catch-ups.
Channel 4's service offers hundreds of hours of programming from current series such as Ugly Betty to classic shows including Father Ted.