The agreement, reached late on Friday following two day of intensive talks in Brussels provides the British prime minister with controversial new powers to restrict EU migrant workers' access to UK welfare payments.
A key UK demand, the so-called Emergency Brake will allow the UK, in "exceptional" circumstances, to restrict certain in-work benefits to EU migrants for four years. The measures will run for up to seven years.
Cameron also negotiated a change to the EU treaties exempting the UK from any future agreements on "ever closer union". The opt-out will acknowledge and guarantee the UK's special status as an EU member state that doesn’t want to deepen political integration.
Commenting on the agreement, Cameron said, "This deal has delivered on the commitments I made at the beginning of this renegotiation process. Britain will be permanently out of ever closer union – never part of a European Superstate."
On the thorny issue of British demands for safeguards against possible discrimination caused by financial rules introduced solely by Eurozone members, Cameron won the ability to allow non-Eurozone members to open discussions on any areas of concern. However the deal does not provide a veto on any 'problem' laws.
On the equally controversial issue of ending the ability of EU migrant workers claiming benefits for children living outside the UK, Cameron had to accept a more watered down agreement, in the face of stiff opposition from Central and Eastern European leaders, where payments will be indexed to the cost of living rate in the home country of the children concerned.
European Council president, Donald Tusk revealed the result through twitter, simply saying, "Deal. Unanimous support for new settlement for #UKinEU."
At a later press conference Tusk added, "The settlement addresses all of Prime Minister Cameron’s concerns, without compromising our fundamental values."
Cameron, during his own press briefing, said, "The EU isn’t perfect. There is a need for further and continuing reform. But the UK is best placed to do that from the inside."
"Our plan for Europe gives us the best of both worlds. And that is why I will be campaigning with all my heart and soul to persuade the British people to remain in the reformed European Union that we have secured today."
Eurosceptic pro-Brexit campaigners were quick to attack the deal, with Ukip leader Nigel Farage tweeting, "This is a truly pathetic deal. Let's Leave the EU, control our borders, run our own country and stop handing £55m every day to Brussels."
Farage added that, "I believe in Britain. We are good enough to be an independent, self-governing nation outside of the EU. This is our golden opportunity."
Cameron will today (Saturday) hold a meeting of his ministers where he will announce the date of the in-out EU membership referendum. That date is expected to be Thursday, 23 June.