She focused on American women and the difficulties they face, the mothers "who hold the country together". In a blatant pitch for the women's vote, she said: "I love you women. You are the best of America. We salute you and sing your praises."
Romney's support among women voters is trailing far behind President Barack Obama.
Ann Romney said bluntly that Americans needed to get to know Mitt Romney, who, she said, is defined by his family, by his faith and by helping others.
Romney's critics contend he cannot talk about his record as Massachusetts Governor because of his healthcare reform used as a model by President Obama. They say he cannot talk about his rescuing of the 2002 Winter Olympics because of the role of federal funds, or about Bain Capital amid accusations that the equity firm he led outsourced American jobs.
Ann Romney went for those who have attacked his success. "It amazes me to see his history of success being attacked. He was not handed success - he built it," she said, referring to the "we built it" theme of the first full day of the convention. A clumsy turn of phrase by Obama, who said during a rally that businessmen did not build successful companies alone, has been a gift to the Romney campaign which exploited it to the full yesterday.
In 2008, the subtext at the Democratic convention was whether America was ready to elect an African American as president. In 2012, the unspoken question at the Republican convention is whether America is ready to vote for a Mormon president, with many conservative Christians harbouring doubts about the faith they consider to be a sect.
Why did her husband not talk about his faith? "This is important," Ann Romney said, wagging her finger. "Mitt doesn't like to talk about how he's helped others because he sees it as a privilege not as a political talking point."
Conscious of the accusations that the Romneys cannot connect with ordinary people because of their huge wealth, Ann Romney took care to point out that she was the granddaughter of a Welsh coalminer. She also referred to her 14 years living with multiple sclerosis and a breast cancer diagnosis in 2008.
The woman known as Romney's "secret weapon" brought the almost exclusively white delegates to their feet, as they shouted "Let's Go Mitt".
Ann Romney was followed to the podium by Governor Chris Christie of New Jersey.
Christie, seen as a future Republican presidential candidate, said: "It's time to end this era of absentee leadership in the Oval Office and send real leaders to the White House."
He said: "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."
Romney and running-mate Paul Ryan were officially declared the party nominees. But there was also some ugly argy bargy on the floor by supporters of libertarian Congressman and failed candidate Ron Paul, highlighting the divisions within the party which has backed Romney more through a sense of inevitability rather than enthusiasm.
It remains to be seen whether Ann Romney - who is more popular than her husband in the polls - can persuade Americans that "this is the man America needs".
