BBC Three is to be dropped from TV schedules and will move online, as part of the BBC's cost-cutting plans.
It means shows such as Don't Tell The Bride and Pramface will only be available through the iPlayer, rather than Freeview, satellite or cable.
The BBC will make an official announcement on Thursday, media correspondent David Sillito said.
Celebrities are already rallying behind the service. Matt Lucas said the move would be "really bad for new comedy".
The BBC's decision follows a speech given by director general Tony Hall last week, in which he said "tough choices" would have to be made if the corporation was to meet its savings target.
"We are in the final stages of a budget process to find an extra £100m of savings," he said at the Oxford Media Convention. "I will announce the outcome of those decisions in the next month."
It is something of a turnaround for Lord Hall, who said in October: "I wouldn't consider closing a channel".
"The public feel very strongly about all the services the BBC runs," he told the World At One. "We have to find other ways [of saving money]".
Before moving BBC Three online, however, the director general must get approval from the BBC Trust, the corporation's governing body, which represents the interests of licence fee payers.
The futures of both BBC Three and BBC Four have been much discussed as the corporation continues to implement its savings plans.
According to industry newspaper Broadcast, moving BBC Three online "would amount to a sizeable step" towards delivering Lord Hall's £100m savings target by 2016.
The channel's service budget was £85m in 2013/14 - although moving the channel online would not eradicate those costs entirely.
"If they want to save money, there will certainly be less programming coming from the BBC Three brand," our media correspondent said.
However, he added, the move to iPlayer would make sense for the station's target audience of 16-34 year-olds.
"Increasingly, it's thought the youth audience are switching to accessing content online. They're watching in their bedrooms and watching on tablet devices."
The move follows the BBC's decision to broadcast select TV shows online ahead of their scheduled TV transmission, among them the latest sitcom from comedian Peter Kay.
Youth channel Radio 1 will also launch as an in-vision channel on iPlayer this September.
Since its launch in 2003, BBC Three has been the birthplace of numerous ratings successes, including Little Britain, Torchwood, Being Human and Gavin and Stacey.
These were among the shows singled out by Little Britain star Lucas in a tweet proclaiming the channel to be "the home of new comedy and drama".
His sentiments were echoed by comedian Jack Whitehall: "I really hope reports that the BBC may kill BBC3 are just rumours. Their support of new comedy in particular is vital."
Comedian Russell Kane, who presents stand-up show Live At The Electric on BBC Three, said the channel "provides a vital part of the entertainment portfolio of the BBC".
"It's not necessarily a youth channel, but it is younger-skewed. I don't see why it should be cut because people who are younger have quieter voices in the political process."
BBC Three's own Twitter feed also joined the protest, posting on Tuesday night: Who knew people love BBC Three more than pancakes?! Feeling loved. #SaveBBC3".
The BBC has previously reversed decisions to close its 6 Music and Asian Network radio services after concerted campaigning by supporters.
However, it has closed several foreign language sections of the BBC World Service, with the loss of more than 650 jobs since 2011.