Romney took the country's first primary with about 38 per cent of voter support, a double-digit victory over his closest rival, Ron Paul. The former Massachusetts governor is the first Republican candidate since 1976 to win the first two GOP contests — the Iowa caucuses and New Hampshire.
"Tonight, we made history," Romney, surrounded by his wife and five sons, told his cheering supporters in Manchester, N.H. "Tonight we celebrate. Tomorrow we go back to work."
Romney's now riding a wave of momentum as he heads to the upcoming South Carolina primary. His campaign is taking on an air of inevitability as he aims to become the Republican who will take on U.S. President Barack Obama in November's general election.
Just as he did in New Hampshire, Romney sits atop the polls in the so-called Palmetto State, home to far more socially conservative primary voters, many of them evangelicals. Those voters were suspicious of both his moderate record and his Mormon faith just four years ago, when Romney unsuccessfully made his first bid for the nomination.
Romney's campaign is getting an additional boost by the fact that none of his rivals are dropping out of the race following New Hampshire. That scatters the vote and puts Romney in a better position to win in South Carolina.
The New Hampshire primary, meantime, represented a huge victory for Paul, the 76-year-old Texas libertarian who won about 24 per cent of the vote to take second place.
"(Romney) certainly had a clear-cut victory but we're nibbling at his heels," Paul said to raucous cheers from his young supporters who chanted "President Paul."
"We have had a victory for the cause of liberty tonight .... We will restore freedom to this country."
Huntsman, meantime, placed third at about 17 per cent. That's good enough for him to stay in the race, he said.
"I think we're in the hunt," the former Utah governor told his supporters as he vowed to continue on to South Carolina.
Newt Gingrich and Rick Santorum trailed the top three at about 10 per cent each, duking it out for fourth place, while Texas Gov. Rick Perry placed last.
For Santorum, in particular, it was a disappointing night.
The staunch social conservative came within a handful of votes of beating Romney in Iowa, but got absolutely no bounce from that victory in New Hampshire, whose primary voters are far more moderate.
Nonetheless, he predicted a better finish in South Carolina, where voters are far more receptive to his views than those in New Hampshire. Gingrich, for his part, has all but declared war on Romney, and warns he'll cause the front-runner trouble in South Carolina.
Romney's victory came despite a full-frontal assault in recent days from his rivals, particularly Gingrich, over his years at the helm of private equity firm Bain Capital — a surprising attack, considering the Republican party has long championed free enterprise and looser government regulations for the financial industry.
Amid the din of the onslaught, Romney's ill-timed remark on Monday — he enjoys firing people, he said as he extolled the virtues of private sector health insurance — didn't help matters, particularly as the United States struggles to recover from an economic recession.
The direct quote — "I like being able to fire people," Romney said — was seized upon by officials at the Democratic National Committee, who did a mash-up video featuring characters like Ari Gold of "Entourage" gleefully telling employees that they'd been canned.
As Romney visited a polling station earlier Tuesday and stopped to cuddle an infant, someone in the crowd yelled out repeatedly: "Are you going to fire the baby?"
But as he revelled in victory hours later, Romney chided his political foes for the Bain attacks, saying they amounted to an assault on capitalism and adding the country already has "a leader who divides us with the bitter politics of envy."
For the most part, however, he took on a tone that sounded decidedly more presidential than his rambling victory speech in Iowa last week.
"Americans know that our future is brighter and better than these troubled times," Romney said.
"The president has run out of ideas. Now he's running out of excuses. And tonight, we're asking the good people of South Carolina to join the good citizens of New Hampshire and make 2012 the year he runs out of time."
South Carolina, however, could remain in play depending on how primary voters there respond to an anti-Romney attack strategy by Gingrich supporters in their state. Pro-Gingrich forces are spending more than $3 million in South Carolina, with the biggest weapon in their arsenal a 30-minute ad that portrays Romney as a ruthless corporate raider during his Bain Capital years.
Such a full-on offensive could do Romney some damage in the state, prompting conservative commentators to tell Gingrich and others to lay off earlier Tuesday.
"To abominate Mitt Romney for having been a success at the business of investing in struggling American companies, connecting entrepreneurs with capital and producers with markets, is foolish and destructive," an editorial on the National Review website read on Tuesday.
"Republicans ought to know better, and the fact that Gingrich et al. apparently do not is the most disturbing commentary on the state of the primary field so far."
Chimed in Phillip Klein, the editorial writer at the right-wing Washington Examiner: "Romney's rivals are engaging in the type of Marxist rhetoric that we're used to hearing from Occupy Wall Street protesters."
A new poll released Tuesday by Public Policy Polling has Romney at 27 per cent in South Carolina, with Gingrich at 23 per cent and Santorum at 18 per cent. The survey also suggested that comedian Stephen Colbert beat Huntsman at five per cent of support compared to four per cent for the one-time China ambassador.