The Prime Minister argued that the deal gave the UK special status within the EU after he negotiated changes to migrant welfare payments and making it easier to block unwanted regulations from Brussels.
The Out camp, which includes Leave.EU, Vote Leave and Grassroots Out, was given a boost by the announcement that London Mayor Boris Johnson will campaign to leave in the run-up to the referendum.
Robert Oxley, head of media at Vote Leave, told PRWeek that the campaign team had already been working "24/7" and had been "on a war footing" long before the announcement.
He added: "They key thing for the campaign was the hours after the deal was announced and we had a strategy around this. The Government wanted to be seen as having agreed something legally binding and our strategy was about pushing back against that, which I think we did successfully."
Oxley said Vote Leave’s campaign had been helped by Monday’s splash in the Metro, which included one of its key messages – ‘time to take back control' - in the headline.
A Grassroots Out spokesman said its campaign had also moved up a gear since the weekend and that 1,000 new people had signed up since the announcement.
"Awareness of our campaign has increased massively," the spokesman added.
But those campaigning to stay in the union were not left flat-footed by the weekend’s developments either.
James McGrory, chief campaign spokesman for Britain Stronger In Europe, said: "The Prime Minister has fired the starting gun on the referendum campaign proper and we hit the ground running with our biggest day of campaigning on Saturday, with 100 activities across the country.
"We are focused on getting out our message to voters that Britain is stronger, safer and better off in Europe. This is a campaign that will be won on facts, not personalities, so it’s our job to highlight the benefits of being Europe to Britain’s economy, to Britain’s security and to Britain’s global leadership."
The Electoral Commission will soon designate an official campaign for either side – Britain Stronger In Europe is likely to prevail on the In camp, but it is less clear who will win the Out designation, and the groups have been at odds in recent weeks.