Mitt Romney has accepted the Republican presidential nomination at the party’s convention in Florida where he has pledged to “restore the promise” of America.
Mitt Romney, 65, accused President Barack Obama of failing to deliver on his promises and presented his plan involving energy independence, cutting the budget deficit and creating jobs.
He also spoke of his Mormon faith.
The Obama campaign said Mitt Romney had been “no tangible ideas” and he “would take our country backwards”.
Mitt Romney will challenge the Democratic president in November’s election.
His speech was the climax of the three-day Republican convention, which correspondents saw as an attempt to show the human side of a candidate who is sometimes accused of being opaque and distant.
Mitt Romney began the most important speech of his political career by accepting the nomination that he was overwhelmingly awarded on Tuesday by thousands of delegates at the gala in Tampa.
It secured him the position that eluded him in his first presidential bid in 2008, when Arizona Senator John McCain became the Republican nominee.
“I wish President Obama had succeeded because I want America to succeed,” Mitt Romney said, in a speech that was watched by millions across the US.
He recounted details of his Mormon upbringing, with anecdotes about his family life and his parents’ loving marriage.
Mitt Romney talked about his own experiences as a father, apparently becoming emotional as he talked about the times when he and his wife Ann would wake up to find “a pile of kids asleep in our room”.
He also levelled a barrage of attacks at President Barack Obama: “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.
Mitt Romney vowed to create 12 million American jobs over the next four years and turn around an economy saddled with an 8.3% unemployment rate.
The presidential nominee also pledged to make the US energy independent by 2020, cut the national deficit and negotiate new trade agreements.
“I will begin my presidency with a jobs tour. President Obama began his presidency with an apology tour,” he said.
Mitt Romney accused the president of having “thrown allies like Israel under the bus”, while being too lenient with Iran.
“Under my administration, our friends will see more loyalty and Mr. Putin will see a little less flexibility and more backbone,” he said.
He brought the crowd to its feet when he pledged to repeal Barack Obama’s signature healthcare bill.
The event ended with the entire Romney family – his wife, five sons and their wives and most of his 18 grandchildren – on stage with him as thousands of balloons were released over the convention floor.
Republicans at the convention said they were confident of victory after the speech.
“It’s been great. It’s fired us up. We’re going forward. We’re going to make it happen,” one delegate said.
“This is just the cherry on the whipped cream, on the ice cream, and we’re going to win in November, and there’s no stopping it now. This is the wind that’s going to blow us into office,” said another.
But Barack Obama’s campaign manager Jim Messina said the address contained little substance.
“Much like the entire Republican Convention, Mitt Romney’s speech tonight offered many personal attacks and gauzy platitudes, but no tangible ideas to move the country forward,” he said.
“What he didn’t share were his actual proposals, which would take our country backwards.”
Appearing on stage earlier to pledge his support for Mitt Romney, Hollywood star Clint Eastwood raised eyebrows with an off-the-cuff monologue to an imaginary Barack Obama in an empty chair.
Referring to the president, Clint Eastwood told a rapturous audience: “When somebody does not do the job, you’ve got to let ’em go.”
Democrats have sought to depict Mitt Romney as a wealthy, elitist, tax-dodging, corporate raider and policy chameleon. Low favorability ratings have dogged him throughout his campaign and he trails Barack Obama in likeability.
To counter that image, the convention heard emotional testimonials about Mitt Romney’s work as a Mormon leader that left some attendees in tears.
One couple talked of how Mitt Romney had befriended and comforted their dying teenage son.
A woman recalled how the Republican’s “eyes filled with tears” when her premature baby daughter was close to death in hospital.
On Wednesday, Mitt Romney’s running mate, Paul Ryan, pledged a “turnaround” for America, while attacking Barack Obama.
But fact-checkers said there were a number of inaccuracies in the Wisconsin congressman’s address.
The job of softening Mitt Romney’s edges also fell to his wife, who brought down the house on Tuesday with a speech about their high-school romance.