Romney won with 39 percent of the vote, a 16 percentage-point advantage against his closest competitor, Texas congressman Ron Paul.
The decisive win in New Hampshire follows a narrow win for Romney in last week's Iowa caucuses, increasing his momentum ahead of the crucial South Carolina primary on January 21.
Speaking to supporters after results showed a decisive win in New Hampshire, Romney was focused on the upcoming South Carolina vote and on the November contest against the current Democrat president, Barack Obama:
"The president has run out of ideas. Now he's running out of excuses," he told a cheering crowd. "And tonight, we are asking the good people of South Carolina to join the citizens of New Hampshire and make 2012 the year he runs out of time."
Not only did Romney meet high expectations in New Hampshire, he emerged with no clear rival to challenge him as front-runner.
Paul finished second with about 23 percent. It was his second strong showing after finishing third in Iowa, the first nominating contest.
But political analysts say Paul remains a long shot for the Republican nomination.
While he has a loyal core of supporters drawn to his libertarian, small-government message, he is seen as being at odds with the Republican Party's more conservative mainstream because of his calls for military cuts, withdrawing troops from Afghanistan, and legalizing drugs.
Analysts say the third-place finisher, former Utah Governor Jon Huntsman, also appears unlikely to win the nomination.
He won 17 percent of the vote in New Hampshire after campaigning intensely there. But he is at the bottom of national polls.
He is not as conservative as his rivals and his role as Obama's first ambassador to China does not endear him to Republicans with harsh views about the current president.
Meanwhile, the three candidates most likely to draw conservative voters -- Newt Gingrich, Rick Santorum, and Rick Perry -- struggled in New Hampshire.
Gingrich, a former speaker of the House of Representatives, and Santorum, a former Pennsylvania senator who came within eight votes of winning Iowa, each won 9 percent on January 10.
Perry considered dropping out of the race after a poor fifth-place finish in Iowa. He effectively skipped campaigning in New Hampshire to focus on South Carolina.
Romney could have a tougher time in South Carolina, which has a large bloc of evangelical Christians.
Some Republicans doubt whether he is sufficiently conservative because of shifting views on abortion and other social issues.
A number of conservative Christians are also wary of Romney's Mormon faith.
But with conservatives failing to rally behind a single candidate, political analysts say their votes could be divided in South Carolina between Gingrich, Santorum, and Romney -- creating an opening for the latter.
with agency reports