Mr Cameron claims his EU reform deal will give 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".
But critics say it does nothing to tackle high levels of immigration or take back powers from Brussels.
UKIP Leader Nigel Farage said: "The 23rd is our golden opportunity, let battle be joined. Mr Cameron keeps on telling us that Britain would be better in a 'reformed Europe'. But he fails to point out that there is no reformed European Union on offer here. The prime minister's EU deal is pathetic."
Britain Stronger in Europe released a campaign video, external accusing leave campaigners of "utter hypocrisy" for attacking Mr Cameron's deal, claiming that many of them have been calling for the same reforms.
The key points of Mr Cameron's reform deal are:
an "emergency brake" on migrants' in-work benefits, with payments phased in during their first four years in a new country, when there are "exceptional" levels of migration. The UK will be able to operate the brake for seven years
child benefit for the children of EU migrants living overseas will now be paid at a rate based on the cost of living in their home country - applicable immediately for new arrivals and from 2020 for the 34,000 existing claimants
The amending of EU treaties to state explicitly that references to the requirement to seek ever-closer union "do not apply to the United Kingdom", meaning Britain "can never be forced into political integration"
The ability for the UK to enact "an emergency safeguard" to protect the City of London, to stop UK firms being forced to relocate into Europe and to ensure British businesses do not face "discrimination" for being outside the eurozone
The Labour Party is officially campaigning for Britain to remain in the EU, although a small group of the party's backbenchers have joined the leave campaign.
Leader Jeremy Corbyn voted for Britain to leave the European Economic Community, as the EU was then known, in 1975 but has since changed his mind, arguing that "it brings investment, jobs and protection for British workers and consumers".
He branded Mr Cameron's negotiations a "sideshow" aimed at appeasing critics in the Conservative Party and said he had missed an opportunity to protect jobs and "stop the spread of low pay".
Scotland's First Minister Nicola Sturgeon said in a statement the SNP will be "leading the positive case to keep Scotland in the EU".