Romney took to the stage at the packed convention center in Tampa, Florida to proffer a polite thank you kiss as part of a carefully choreographed attempt to reintroduce the sometimes awkward candidate as a loving family man.
The 65-year-old multi-millionaire businessman will formally take up the nomination with his all-important acceptance speech on Thursday, the climax of three days of rousing convention addresses by party grandees and rising stars.
Romney lies neck-and-neck with Democratic President Barack Obama in national polls ahead of a November election that should be the challenger's for the taking, given the sour economy and stubbornly high unemployment.
Romney's campaign has been eager to promote the gregarious, 63-year-old Ann as a conveyer of the family story, a mission intended to humanize a candidate who trails Obama badly in terms of likability and can come across as stiff.
She delivered her side of the bargain, blending a targeted pitch to vital women voters with a personal narrative about Mitt that dwelt largely on their all-American love story, their wholesome family and his winning attitude.
"This man will not fail," Ann Romney said, staring in determined fashion right at the lens in an address beamed live into American living rooms just 10 weeks before voters go to the polls.
"This man will not let us down. This man will lift up America!"
After a series of wealth-related gaffes during the campaign, she invoked their love story as high school sweethearts as she sought to portray them as an everyday couple who shared hardships just like other Americans.
"It has been 47 years since that tall, kind of charming young man brought me home from our first dance. Not every day since has been easy. But he still makes me laugh," she said.
"You can trust Mitt... He loves America. He will take us to a better place, just as he took me home safely from that dance."
Earlier, in a state-by-state roll call of delegates on the convention floor that reflected the results of the Republican primary elections, Romney soared past the 1,144 threshold to formally earn the nomination.
But an ABC News/Washington Post poll released late Tuesday found that Romney still lags in favorability, with 40 percent of Americans viewing him "favorably overall" while 51 percent view him as unfavorable.
That's considerably worse than Obama, who enjoys a 50-47 percent rating, and Romney's is the lowest favorability rating of any major party nominee at the time of the convention since at least 1984, the pollsters said.
Charismatic New Jersey Governor Chris Christie followed Mrs Romney on stage, giving the keynote address and firing up the crowd with a tear-down of Obama that failed to hide his own ambitions for a potential presidential run in 2016.
The convention kicked off earlier Tuesday with the usual blend of political theater and razzmatazz despite the hurricane bearing down on New Orleans, which derailed Monday's opening and still threatened to cast a pall over proceedings.
Many Americans do not tune in until the convention season starts -- Obama and the Democrats hold theirs next week in Charlotte, North Carolina -- so Tampa provides Romney with a golden opportunity to buff up his image.
The run-up to the convention was marred by incendiary remarks from Todd Akin, a Republican congressman seeking a Senate seat in Missouri, who suggested women's bodies spontaneously prevent pregnancy after a "legitimate rape."
The Romney camp, which roundly condemned the remarks, is keen to get back on message, pressing the case that the former Massachusetts governor understands the economy better than Obama and knows how to get the country back on track.
Republican delegates said Romney was on course to take the White House as the American people recognized Obama's "hope and change" mantra had worn thin after four years of economic hardship.
"The president can smooth talk anything but I think nobody wants to listen to that anymore," Tina Gibson from Texas, wearing a star-spangled banner outfit complete with cowgirl hat, told AFP on the convention floor.
Obama has broken with tradition and is campaigning hard through his rival's event, countering Romney's bid to monopolize the media spotlight.
"This week in Tampa my opponents will offer you their agendas. It should be a pretty entertaining show -- I'm sure they will, you know, have some wonderful things to say about me," he said Tuesday in the key swing state of Iowa.
"But what you won't hear from them is a path forward that meets the challenges of our time."
Watch the full video of Ann Romney's speech below, originally uploaded to YouTube on August 28, 2012:
