The channel, which was the original home to such comedy shows as 'Bad Education', 'Little Britain' and its longest-running show 'Two Pints Of Lager And A Packet Of Crisps', will run as a promotional channel for February, with the final switch off coming at the end of February.
The BBC hope to save £30million with the move, money they intend to plough into an extended drama budget.
'Bad Education' starring Jack Whitehall was BBC3's highest-ever rated comedy debut, when it first aired in 2012
However, the BBC Trust have added some conditions to their agreement to the move, namely that all of the new online channel's long-form programmes get a showing on BBC One and BBC Two "at a variety of times", ie. not just buried in out-of-hours slots and rendered all but invisible.
The Trust has also stipulated that the BBC must cater more to younger audiences on BBC One and BBC Two, in addition to those programmes originally created for BBC3.
'Two Pints of Lager and a Packet of Crisps' was another long-running hit for the channel
These conditions have been put in place to try to minimise the deficit in youth audiences created by the demise of BBC3, which currently reaches an estimated 11.2million viewers a week.
Channel Controller Damian Kavanagh writes in a BBC blog today, "BBC3 is not closing, we are reinventing it online. “We will no longer be limited to traditional TV. These are exciting times for BBC3.”
There is no news as yet on what will replace BBC3's place on the linear spectrum, with the BBC given a further three months to return to the Trust with a plan. The proposition they initially mooted, for BBC1 + 1, was rejected on the grounds it would be unfair to commercial rivals. Any potential broadcasters will have a bit less time to play with, however, as the Trust accepted grounds to extend CBBC's hours of broadcasting until 9pm.
Today's decision comes after a tireless campaign to keep BBC3 on air, including a petition signed by 300,000 viewers. Comedy producers Jimmy Mulville and Jon Thoday even offered to buy the channel from the BBC, a move they explained was to protect the comedy production industry, with the BBC one of the main distributors of independent content, but the BBC said it wasn't for sale.
Only a fortnight ago, Channel 4 chief executive David Abrahams told media journalists that his station's comedy output could be compromised, along with its current affairs coverage and drama investment, if the channel is privatised - a move that has been the subject of much speculation among media watchers, even though David Abrahams explained he had only had one single chat with the Government, who are the owners of the station.