Taking centre stage with an address to the Republican convention in Tampa, Florida, Romney will vow to be a champion for small business and to restore a sense of innovation in America.
"What is needed in our country today is not complicated or profound. It doesn't take a special government commission to tell us what America needs. What America needs is jobs. Lots of jobs," Romney will say, according to excerpts of his speech released by the campaign.
Romney's speech accepting the presidential nomination will be seen by a television audience in the tens of millions, with some voters getting their first extended look at the former Massachusetts governor.
In his speech, he plans to slam Obama's record as president, drawing a sharp comparison between the promise of his election in 2008 and the "disappointment of the last four years."
"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," he said. "President Obama promised to slow the rise of the oceans and to heal the planet. My promise is to help you and your family."
The speech is Romney's toughest test yet in his bid to win the White House at the Nov. 6 election.
A multimillionaire former businessman who can often come across as stiff, Romney will strive to inspire his fellow Republicans who have at times shown little passion for him, and make the broader electorate feel more comfortable with him.
As portrayed by Democrats, Romney, 65, is alternately a heartless corporate raider, wealthy elitist, tax evader and policy flip-flopper who should not be trusted with the keys to the White House.
To counter that image, Romney's speech includes biographical passages describing his parents and family and defending his work at Bain Capital, the private equity company that critics have accused of raiding companies and cutting jobs.
"That business we started with 10 people has now grown into a great American success story. Some of the companies we helped start are names you know," he said, naming Staples and Sports Authority.
Romney and Obama have been running close in polls, but the convention so far has given Romney a boost. The latest Reuters/Ipsos online poll showed him moving into a narrow lead over Obama -- 44 percent to 42 percent among likely voters. The Republican had entered the week trailing Obama by four percentage points.
Such convention-related boosts in the polls are typically short-lived, and with Obama set to headline the Democratic convention next week in Charlotte, North Carolina, the incumbent could quickly rebound.
Obama still has the advantage over Romney in likability, an important trait that may mask other problems Obama has in persuading voters to give him four more years as a weak economy continues to dog the country.
'A TOUCH OF HOLLYWOOD'
Movie star Clint Eastwood will bring a touch of Hollywood glamour to the convention, appearing as a surprise, last-minute speaker to warm up the crowd for Romney, a Republican official said. Romney's speech will start at around 10:15 p.m. (0215 GMT).
Leaving little to chance at the carefully stage-managed event, organizers extended the podium outward and lowered it closer to the audience, seeking to create more intimacy for Romney's address within the cavernous hockey arena.
Dropping in on the convention hall, Romney stood at the podium while workers adjusted teleprompters to his preferred height and a convention organizer took him through his paces.
"This is the biggest speech of his political career, and I have no doubt that he will deliver the best speech of his political career," senior campaign adviser Eric Fehrnstrom told reporters.
Romney's nomination culminates a long journey. After failing to win the Republican nomination in 2008, he plotted a return to the political arena. This year he was tested time and again by a series of conservative alternatives from Newt Gingrich to Rick Santorum in a long and bitter primary campaign.
He outlasted all of them, helped by huge spending on negative ads by "Super PACs" that support him, but is still struggling to win over many Republicans unsure of his conservative credentials.
