"I full well believe I'm going to win," Perry told South Carolina voters on a conference call about an hour before he planned to kick off the campaign with a speech in Charleston.
Perry criticized President Barack Obama on foreign policy and said he would do better at creating jobs. Perry said he would go to Washington to do his duty and not make friends.
Perry's speech was set for 1 p.m. EDT at a conservative conference, only a few hours before the release of results from the straw poll in Iowa, the nation's first caucus state. Former Minnesota Gov. Tim Pawlenty and U.S. Rep. Michele Bachmann of Minnesota are hoping for a boost.
"I have never seen this landslide of emotion for a candidacy. I cannot literally keep up with the emails and messages coming into my cellphone," said Katon Dawson, a former GOP chairman in South Carolina who's a Perry supporter.
"There is an excitement for Gov. Perry that there just isn't around the other candidates."
Perry, 61, was to visit New Hampshire, the first-in-the-nation primary state, later Saturday before stepping onto Iowa soil Sunday.
The leading GOP candidate so far has been Mitt Romney, a former Massachusetts governor making his second run for the nomination. But no one in the field has managed to raise the kind of enthusiasm among conservatives that seems to surround Perry.
Among the others in the race are former Utah Gov. Jon Huntsman, former U.S. House Speaker Newt Gingrich, U.S. Rep. Ron Paul of Texas, former U.S. Sen. Rick Santorum of Pennsylvania and businessman Herman Cain.
Through three terms as governor, Perry has overseen significant job growth in his state while working to keep taxes low. He was an early backer of the tea party movement. He enjoys the support of social conservatives because of his opposition to abortion and gay rights. He is also an evangelical Christian who organized a well-attended prayer rally in Houston last week.
Perry is a prodigious fundraiser who has begun laying the groundwork for a national finance network that supporters say would rival President Barack Obama's. Obama is expected to exceed his record $750 million haul from 2008.
But some Republicans worry that Perry's hard-core conservatism and Texas style may not play well in a 50-state contest, particularly so soon after another Texas governor, George W. Bush, served in the White House.
Bush had record low approval ratings when he left office in 2009.
Perry's visit to New Hampshire was to be his first of the year, on the heels of a visit by some state activists to Texas to encourage him to run.
Romney has dominated early polling in New Hampshire, where he has a summer home and has devoted much of his campaigning so far.