Addressing the final party conference before the General Election, he insisted he was ready to become Prime Minister and promised doubting voters the party had changed for good but admitted voters still had "big questions" about the Tories.
He urged activists to have the "confidence" they were right to start tackling the 175bn budget deficit straight away to avoid a "deeper and darker recession", as he accused the Government of being locked in a "dance of death" which risked "dragging our whole country down".
Seeking to ease party nerves after its opinion poll lead was slashed to two points, he said: "It's an election we have to win because our country is in a complete mess and it's our patriotic duty to turn this around and give our country a better future."
He added: "They don't hand General Election victories and governments on a plate to people in this country, and quite right too.
"This election was always going to be close, this election was always going to be a real choice – Labour or Conservative, Gordon Brown or me.
"And this election was always going to be a real fight for our party, a fight to make sure we serve the country we love and that is the fight that we are going to have."
Yesterday's speech at the party's spring conference in Brighton was the final time Mr Cameron will address such a large gathering of members before the General Election, expected to be on May 6.
With the economy at the heart of the election battle, Mr Cameron accused the Prime Minister of "incompetence" and said: "At this coming election we're going to take out your record and tear it apart piece by piece."
He told voters they were faced with a choice between another five years of Gordon Brown – which would be "a disaster for our country" – or a Tory party "that has got the energy, leadership and values to really get this country going again".
Mr Cameron also promised the most family-friendly manifesto a political party has ever offered including proposals to recognise marriage in the tax system.
He pledged to always stand up for the NHS and said his government would be based on aspiration, responsibility and giving people more power over their lives.
In a message to critics of his modernisation moves – trumpeting more women and ethnic minority candidates – he insisted the party would never turn back but there were significant parts of the speech targeted to traditionalists as he vowed to tear down Labour's regional structures, tackle immigration and deny benefits to those who refuse to work.
Pledging to tour the globe to drum up business for the country, he added: "I want a real clear message to go out that Britain is under new economic management and we're open for business."
He also sought to inject a note of optimism, describing the British people as "amazing" who "don't get knocked down we get up and fight".
"I want you to think of the incredible dark depression of another five years of Gordon Brown and say no, we're not going to do that," he said. "So come on, let's get out there and win it for Britain."
Liberal Democrat home affairs spokesman Chris Huhne said the speech was short on specifics and on the key assurance of fairness that was essential in tackling economic problems.
Work and Pensions Secretary Yvette Cooper, Labour MP for Pontefract and Castleford, said Mr Cameron had shown himself to be merely a "salesman" and added: "He didn't really tell us anything serious about what he was actually selling though.
"People will take a long hard look at that speech but also what the Conservatives are offering and really find it wanting."