The deal gives the UK “special status” within the EU, Cameron said at a late-night press conference after the negotiations were finished. Britain will be out of the “ever-closer union” - the process of continuing economic and political integration of EU member states - and the UK won’t be part of what Cameron calls a “European superstate”.
The British prime minister says there will be “tough new restrictions “ on access to Britain's welfare system for EU migrants with “No more something for nothing.”
Moreover, Cameron said Britain will “never” join the euro single currency and that he has secured “vital protections” for Britain's economy.
Critics say that Cameron fought the EU merely for the sake of domestic politics.
“There is a civil war in the Conservative Party,” says Richard Corbett, vice-chairman of the Socialist bloc in the European parliament.
Cameron was forced to make concessions on one of the most difficult items: social benefits for EU migrants working in the UK.
Initially he wanted a 12-year grace period before EU immigrants could have social benefits in the UK. He went then down to seven and finally had to settle for four years.
But he did obtain the right for the UK to send back EU migrant who did not find work within six months, and send back criminals altogether.
The question is now whether what Cameron has negotiated be accepted by his Conservative Party.
“The neo-liberal right hates the EU on ideological grounds, they hate the fact of the Single European Market as a market with rules, to protect workers, to protect consumers, to protect the environment, to ensure fair competition.
“Then there is a relatively more moderate wing of the Conservative Party, that realises that this would be very damaging to Britains economic interests and it would be a disaster for the country to leave the EU.”
Cameron will now fight for the UK to stay inside the Union in the months leading up to the referendum on 23 June. But the outcome of that is far from clear.
“Cameron’s reforms may have some improvements,“ says Corbett but they are by no means a guarantee that voters are now convinced to stay within the EU.
“If at the referendum there is a No vote, there would be a long process, two years of negotiations, for exiting the EU," says Guntram Wolff, director of the Brussels-based thinktank Bruegel Institute. “And these two years would involve already a significant economic cost both for the UK as well as for the rest of the EU.”
Leaving the EU will have a dire effect, according to Wolff.
“A No vote in the referendum would have pretty immediately negative consequences both for the UK economy as well as for the European economy,” he says.
British scepticism about the EU has existed since the country's accession to the European Community in 1973.
British people “never held the EU close to their heart, unlike other countries such as Germany, France or Italy,” says Wolff, pointing out that the founding principles of the Union tend to become more and more blurred to young generations.
“The idea of overcoming the war period was very important at the first 30-40 years of the EC,” says Wolff. “But nowadays it has to be a different logic. Today there is the question of can the EU help us globally, to be a better player.“
“It is extremely important that the UK cannot deal alone with for instance China. China is just too big, we need to join forces, if you want to defend some of the European interests towards China"
Wolff is also worried about the growing mistrust in European institutions. Not only in the UK but in Europe as a whole.
“I think we have a democracy crisis at hand,“ he says. "Less faith in the political elites and people turning to populists.
“I think what they have to learn is to collaborate much more effectively together cross border to actually show that populists can not provide the answers but they can provide the answers.”
In London Nigel Farage, the leader of the populist Ukip party, was quick to criticise Cameron’s deal as "not worth the paper it's written on".
David Cameron has a tough four months ahead of him.