He said he would be campaigning to remain in a reformed 28-nation bloc.
A string of ministers have come out in favour of remaining, but others will campaign against Cameron.
Home Secretary Theresa May heads the list of those who have announced they will campaign to stay, but Justice Secretary Michael Gove has signed up to the leave campaign, the BBC reported.
Leave campaigners are also hoping London Mayor Boris Johnson will join their cause but he is yet to declare where he stands.
Cameron said that his EU reform deal, hammered out at a two-day summit in Brussels, will give the Britain "special status" within the bloc, tackling concerns over migrants getting "something for nothing" from the benefit system and exempting the country from the EU drive for "ever closer union".
He argued that Britain would be "safer, stronger and better off" in the EU and warned that leaving the EU would be a "leap in the dark" as he appealed to voters to back his reform deal
"Leaving Europe would threaten our economic and our national security," he said.
The date of the referendum still has to be formalised by parliament, where Cameron will deliver a speech on Monday.
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