Romney, a former governor of Massachusetts, collected 2,061 votes by the time Wyoming announced its delegate vote.
Applause erupted after New Jersey announced its 50 votes, putting Romney over the 1,144-delegate threshold to secure the nomination. Alabama cast the first vote, announcing all 50 of its delegates for Romney.
The strains of "Shout" filled Tampa Bay Times Forum as delegates waved blue-and-white "Mitt" placards and chanted "Mitt!" and "Let's go, Mitt!" as images of the party's standard-bearer in November flashed across the screens on the stage.
"America needs a real leader and real change," John Sununu, a former governor of New Hampshire, said in his speech to place Romney's name in nomination.
"Now we are here to affirm a leader who will produce that change," Sununu said.
Ron Paul, the retiring libertarian U.S. representative from Texas, collected a smattering of votes, including the majority of the votes from Iowa, Minnesota and Nevada.
Several states cast votes for Rick Santorum, a former U.S. senator from Pennsylvania.
Ryan, King said, is "a man who can help us believe in America again."
Ryan is a "critical leader" the country needs now, said King, who like Ryan is from Janesville.
"Mitt Romney believes that. Do we?" King said, when nominating Ryan.