Romney, the presumptive Republican presidential nominee, praised Walker's leadership and said his approach to limiting government and slashing spending in his state was a stark contrast to President Barack Obama.
"At the national level we can learn a lot from this guy," Romney said after Walker introduced him to an overflow crowd in the parking lot of a Janesville textile mill on the fourth day of Romney's bus tour of battleground states.
"If you're responsible, and you don't spend more money than you take in, and you're very careful in making sure that your budget is balanced, and you have a very pro-business attitude, encouraging businesses to come in and grow, then it's good for jobs and the American people," Romney said.
Romney's embrace of Walker marks his campaign's growing confidence that he may be able to win Wisconsin in the November 6 election, though the state has long been seen as likely to chose Obama.
Walker became a hero to conservatives in the last
year for his sledgehammer approach to reining in public-sector unions and cutting spending. He survived a recall effort by state Democrats earlier this month.
"We were able to show here in Wisconsin that you can turn things around," said Walker, who introduced Romney at the textile mill rally and declared he was "proud to still be your governor."
Polls show Obama and Romney, a former Massachusetts governor, in a tight race for the White House, with worries about the slow economic recovery hurting Obama's approval ratings.
Romney has focused on his past as head of a private equity firm to argue that he would provide better economic leadership. Like Walker, he often employs anti-union rhetoric.
Wisconsin Republicans Energised
Romney's five-day bus tour has focused on a half-dozen swing states - New Hampshire, Ohio, Pennsylvania, Wisconsin, Iowa and Michigan - that could be critical in the November election.
Wisconsin has backed Democrats at the presidential level since 1984, and Obama won comfortably here in 2008. But recent polls show a tight race in the state, and Walker's recall victory has energized Wisconsin conservatives.
Romney said Obama was taking the state for granted and predicted a victory in the general election.