David Cameron says a deal struck with EU leaders will give the UK "special status" and he will campaign with his "heart and soul" to stay in the union.
He added it also included changes to EU treaties and would be presented to his cabinet at 10:00 GMT.
EU exit campaigners said the "hollow" deal offered only "very minor changes".
The agreement on renegotiating the UK's EU membership was announced by European Council president Donald Tusk, who tweeted: "Deal. Unanimous support for new settlement for #UKinEU."
It paves the way for the UK to hold an in/out referendum on EU membership, which has been promised by the end of 2017 but is expected in June this year.
Mr Tusk said it "strengthens Britain's special status", while EU Commission president Jean-Claude Juncker described it as "fair".
Mr Tusk added: "We didn't walk away from the negotiating table. We were willing to sacrifice part of our interests for the common good, to show our unity.
"I deeply believe the UK needs Europe and Europe needs the UK. But the final decision is in the hands of the British people."
Read more: EU deal gives UK special status, says PM - BBC News