"We will devote Wednesday night to showing the country that Mitt Romney's 'Plan for a Stronger Middle Class' will restore our country as the best place in the world to find a job, start a business or hire a worker," Republican National Committee Chairman Reince Priebus said in announcing the day's theme and speakers.
The prime-time part of the convention would "show that the Romney approach is both optimistic and achievable," he said.
New Jersey Gov. Chris Christie later told delegates Romney would tell the nation the "hard truths" it needed to hear "to put us back on the path to growth and create good-paying private-sector jobs again in America" and "to end the torrent of debt that is compromising our future and burying our economy."
Wednesday's convention theme is "We Can Change It." Tuesday's was "We Built It," intended as a jab at President Barack Obama's July 13 assertion that government played a big role in business success because it built roads and bridges and invested in research that went into building the Internet.
"Big government didn't build America. You built America," Virginia Gov. Bob McDonnell said to delegate cheers.
The Tuesday theme also drew ironic remarks from some TV commentators who pointed out the Tampa Bay Times Forum, where the convention is being held, was built with 62 percent government funds.
McDonnell also said the party platform approved Tuesday "projects a sea change in the way that government works."
The platform -- a list of the actions the party supports -- includes calls to ban abortions and gay marriages, to turn Medicare into a voucher system and to cut taxes. It also said the party would oppose gun-control legislation.
Romney and running mate Paul Ryan were both officially nominated as the presidential and vice presidential candidates Tuesday.
Their nominations become official Thursday, when the vote is accepted by the convention chairman.
"This man will not fail. This man will not let us down," Ann Romney said of her husband of 43 years. "This man will lift up America."
She also said their years together were not "a storybook marriage."
"No, not at all. What Mitt Romney and I have is a real marriage," she said.
At the end of her address, her husband made his first appearance at the convention, joining her onstage to the strains of the song "My Girl."