The Prime Minister made the long-awaited announcement after meeting with minsters at Downing Street to discuss reforms he secured yesterday following two days of talks in Brussels.
It was the first time the UK’s cabinet has met on a Saturday since the Falklands War more than 30 years ago, showing the significance of the occasion.
EU referendum timeline
Ministers are now free to publicly back the “leave” campaign and Michael Gove, Iain Duncan Smith and Chris Grayling are believed to be among those opposing the Government’s official stance.
Mr Cameron has vowed to campaign for Britain to stay in the 28-nation bloc “with all my heart and soul” after securing a package of changes with European leaders.
He said the reforms, which include curbs on EU workers' benefits, protections for non-euro nations and an opt-out from “ever closer union”, cemented Britain's “special status” despite a series of compromises.
Nigel Farage dismissed the “truly pathetic deal” and urged voters to seize the “golden opportunity” to vote for a Brexit, which is Ukip’s foundational principle.
Jeremy Corbyn dismissed Mr Cameron's re-negotiation as a “sideshow” but confirmed Labour would be campaigning for an ”in“ vote.
"Despite the fanfare, the deal that David Cameron has made in Brussels on Britain's relationship with the EU is a sideshow, and the changes he has negotiated are largely irrelevant to the problems most British people face and the decision we must now make," he said.
"We will be campaigning to keep Britain in Europe in the coming referendum, regardless of David Cameron's tinkering, because it brings investment, jobs and protection for British workers and consumers."