Six Tory MPs pledged their commitment to restoring Britain's "sovereignty" as they announced they would be campaigning for the country's exit from the the EU.
Minutes after David Cameron announced the date for the referendum, Michael Gove, Iain Duncan Smith, Chris Grayling, Theresa Villiers, John Whittingdale and Priti Patel made the journey across the river to the headquarters for exit campaign group, Vote Leave.
They arrived to cheers from supporters and were quick to sign a banner emblazoned with the slogan: "Let's take back control".
Chris Grayling, Leader of the House of Commons, expressed his relief at finally being able to formally take a public stance on the issue "after all these weeks of not being able to say anything".
He said that talks in the Cabinet meeting had been "deeply civilised" and that they had "agreed to have a mature, sensible, grown-up, friendly debate about these matters over the next few months".
Gesturing towards his colleagues, Mr Grayling continued: "The six of us who stand here today are committed to campaign for Britain to leave the European Union.
"This is going to be a team effort. It is not going to be Conservative effort, it is going to be a cross-party effort, it is going to involve people of all parties and none.
"But above all, it is a campaign to restore the sovereignty of our nation."
While recognising that it would take the efforts of those up and down the country, he declared the campaign would be successful in securing the vote for Britain to leave the EU.
Mr Grayling thanked those present - many of whom will voluntarily spend the weekend calling councillors and asking for their support - "for being part of a team that is going to be a winning team and for starting on a journey that I think will take Britain to a prosperous and successful independent future".
Earlier Nigel Farage dismissed the Prime Minister's deal as "truly pathetic" as he urged voters to take the "golden opportunity" to get the UK out of the EU.
But the Ukip leader faced controversy after unveiling firebrand left-wing former Labour and Respect Party MP George Galloway as the latest recruit to the Brexit campaign.
Mr Farage returned from Brussels to address a packed anti-EU rally put on in Westminster by the cross-party Grassroots Out (GO) group - which is seeking recognition as the official "leave" campaign.
The event had been seen as a likely platform for Eurosceptic cabinet ministers to announce their intention to campaign for "leave", but the delays in Brussels scuppered that prospect.
Reacting to the deal, Mr Farage said: "I believe in Britain. We are good enough to be an independent, self-governing nation outside of the EU. This is our golden opportunity.
"This is a truly pathetic deal. Let's Leave the EU, control our borders, run our own country and stop handing £55 million every day to Brussels."