Ann Romney tells Republicans Mitt 'will not fail'
Mitt Romney's wife, Ann, has painted a loving portrait of her husband at the Republican convention, on the day he became the party's White House nominee.
In her prime-time speech, the would-be first lady spoke of her "real marriage" to a steadfast partner and father.
Correspondents say the address aimed to show the human side of the Republican, who lags behind President Barack Obama in likeability ratings.
Mr Romney will challenge the Democratic president in November's elections.
Opinion polls show Mr Obama neck-and-neck with Mr Romney, who will deliver his big speech to the convention on Thursday.
Tuesday's proceedings came to an end with a tubthumping speech by New Jersey Governor Chris Christie, who told delegates in Tampa that Mr Romney would tell Americans "the hard truths" they needed to hear as he sought to fix the economy.
'From my heart'
Highlighting Mr Romney's image problem, a new opinion poll suggests the former Massachusetts governor's favourability rating is the lowest of any major party nominee since Ronald Reagan's presidency.
Mrs Romney, 63, told the audience she wanted to "talk to you from my heart about our hearts", saying of her husband, "you really should get to know him".
She talked about the way her husband helped her deal with multiple sclerosis and breast cancer.
"I read somewhere that Mitt and I have a 'storybook marriage,'" she said.
"Well, in the storybooks I read, there were never long, long rainy winter afternoons in a house with five boys screaming at once. And those storybooks never seemed to have chapters on MS [multiple sclerosis] or breast cancer.
"A storybook marriage? No, not at all. What Mitt Romney and I have is a real marriage."
She addressed criticism from Democrats over her husband's successful private equity career. "Mitt will be the first to tell you that he is the most fortunate man in the world.
"But as his partner on this amazing journey, I can tell you Mitt Romney was not handed success. He built it."
Mrs Romney ended by pledging: "This man will not fail. This man will not let us down.
"He will take us to a better place, just as he took me home safely from that dance."
Mr Romney, 65, appeared on stage and kissed his wife as she concluded her remarks, to a standing ovation from the audience.
Speaking after Mrs Romney, Chris Christie stressed that Mitt Romney was right man to take control of a struggling US economy.
"Mitt Romney will tell us the hard truths we need to hear to put us back on the path to growth and create good paying private sector jobs again in America," he said.
"It's time to end this era of absentee leadership in the Oval Office and send real leaders to the White House."
Abortion and Wall Street
The speeches followed a roll-call of party delegates and a lively voice poll in which state delegates called out their team's allocation of votes.
Altogether, Mr Romney secured 2,061 votes, bringing him comfortably over the crucial 1,144 delegates needed to clinch the nomination.
Vice-presidential candidate Paul Ryan was also given the Republican party's official stamp of approval on Tuesday. He will speak to the convention in a much-anticipated speech on Wednesday night.
There were attacks on Mr Obama, with House Speaker John Boehner saying "his record is as shallow as his rhetoric".
Republican National Committee chairman Reince Priebus said the president has "never run a company. He hasn't even run a garage sale or seen the inside of a lemonade stand".
The convention also approved its party platform - a policy agenda that calls for tax cuts to revive the economy, repealing and replacing a healthcare law passed by Mr Obama, and an end to abortion.
Recent opinion polls have indicated that voters view the economy and unemployment, which is stuck at 8.3%, as top priorities.
The platform also calls for the overturning of measures passed to regulate Wall Street in the wake of the 2008 economic collapse.
This is Mr Romney's second run for the White House, after an unsuccessful bid in 2008.
President Obama's re-nomination will be confirmed next week at the Democratic National Convention in Charlotte, North Carolina.
This year's convention got off to a late start when Monday's programme was postponed amid concerns that Hurricane Isaac might disrupt the proceedings in Tampa.
But the category one hurricane missed Tampa, instead making landfall in southern Louisiana on Tuesday evening.
It comes almost seven years to the day since Hurricane Katrina devastated New Orleans.