The expression of support for his former foe is a quick turnabout for the former Minnesota governor, who earlier this summer lampooned Romney over his healthcare reform plan, which Pawlenty called "Obamneycare."
Pawlenty announced his decision in an email Monday morning -- just hours before the GOP contenders are scheduled to meet for another debate.
"Alone among the contenders, [Romney] possesses the unique qualifications to confront and master our severe economic predicament," Pawlenty wrote. "His abiding faith in our country's exceptional historical position as a beacon of freedom will make him the most important leader in a world that depends upon a strong America to stay at peace."
In an interview Monday morning on Fox News Channel, Pawlenty said that Perry's rhetoric on Social Security -- which he has called a "Ponzi scheme" -- made him a flawed candidate.
"Governor Romney wants to fix Social Security -- he doesn't want to abolish it or end it," Pawlenty said. "He doesn't believe it should be thrown out -- he thinks it should be reformed and fixed."
During an appearance on "Fox News Sunday" in June, Pawlenty had leveled an attack on the then-front-runner over his support for a health insurance mandate in Massachusetts. The plan he enacted in the Bay State laid the groundwork for the national healthcare reform effort President Obama pursued, Pawlenty argued, saying the plans were so similar they could be called "Obamneycare."
One of the crushing blows to Pawlenty's campaign came just days later when he failed to follow through on that attack. In a New Hampshire debate, Pawlenty was reluctant to make the same critique of Romney when they shared the same stage.
He attempted to renew that attack in person in August during another debate in Iowa, but his moment had passed.
In an interview on "The Colbert Report" last week, Pawlenty explained his initial reluctance to attack Romney in person by saying that voters had already factored in his healthcare plan in their consideration.
In the Fox interview Monday morning, Pawlenty said his early show of support was not a first effort to join an eventual Romney ticket as the vice presidential nominee.
"I was down that path once before, with John McCain, and I'm not even going to consider that," Pawlenty said. "I'm going to do what I can to help Mitt in this race, but that won't be part of the future for me."