Mitt Romney has vowed to restore the promise of America as he formally accepted the Republican presidential nomination.
Delivering the closing speech at the Republican Party's Florida convention, Mr Romney promised to create millions of jobs, cut debt, make the US energy self-sufficient and get tough on Iran.
The candidate declared that Barack Obama had failed to deliver on his promises of hope and change and that it is time for a new leader to help America through tough times.
"President Obama promised to begin to slow the rise of the oceans, and heal the planet. My promise is to help you and your family," he said.
"The time has come to turn the page. Today the time has come for us to put the disappointments of the last four years behind us. To put aside the divisiveness and the recriminations. Now is the time to restore the promise of America,"
He added: "I want to succeed because I want America to succeed. Now is the moment we can do something."
Mr Romney, who has been criticised for being too stiff and distant, recounted details about his youth as a Mormon and then a married man with five sons.
He choked up at least twice, including when he recalled how he and wife Ann would wake up to find "a pile of kids asleep in our room".
His acceptance of his party's nomination was the climax of the three-day convention and a milestone in his long, often rocky quest for the presidency.
He claimed the nomination honour he was denied when John McCain won four years ago, under the theme of "We Believe In America".
This year, he has had to fend off a series of Republican challengers, questions about his shifting positions and mutterings about his Mormon religion.
Polls show Mr Romney and Mr Obama in a dead heat, with the economy the biggest issue in the campaign.
The US is struggling with 8.3% unemployment and the slowest economic recovery in decades but Mr Romney promised to create 12 million new jobs.
He said: "You know there's something wrong with the kind of job he's done as president when the best feeling you had was the day you voted for him."
Seeking to show foreign policy mettle, Mr Romney said Mr Obama had thrown Israel "under a bus" and promised to get tougher with Russia's Vladimir Putin.
He also sought to exploit the background of Mr Obama - who is a constitutional lawyer - for a lack of business experience amid the worst downturn since the 1930s.
After the speech, Mr Romney's extended family, including his sons and numerous grandchildren, took to the stage as red, white and balloons rained down amid wild applause.
Sky Political Editor Adam Boulton said: "It was a powerful and passionate speech. "The message really was summed up in the phrase, 'My promise to help you and your family'.
"His other theme was disappointment with the Obama administration."
Ahead of the key address, the crowd in Florida cheered avidly as veteran actor and director Clint Eastwood urged America to vote for Mr Romney.
Eastwood mocked Mr Obama in an imaginary interview with the president and he told delegates many people in Hollywood - known for its Democrat preference - wanted a businessman to lead the nation.