Just a year later, Romney emerged as a leading voice against gay marriage, opposing the Massachusetts Supreme Judicial Court's ruling overturning the ban on same-sex marriage.
With his positions evolving on everything from abortion to gay rights, stem cell research to health care, Romney has prompted charges of political opportunism from Republicans and Democrats alike.
In a Web video last month, Texas Gov. Rick Perry highlighted Romney's shifts on health care and illegal immigration and reminded voters, "You cannot lead a nation by misleading the people."
Romney's answer from Wednesday's debate: "I think people understand that I'm a man of steadiness and constancy."
To counter the criticism, he said he's been married to the same woman for four decades, has been a member of the same church his entire life and worked at one company for 25 years.
Romney - who is leading opinion polls in the GOP race - hopes that the argument will help him get beyond what dogged his 2008 campaign.
This time, the electorate's focus on the troubled economy may overshadow Romney's shifts. The former venture capitalist and Harvard Business School alumnus is counting on it as he plays up his business experience.
"With the economy being the absolutely overriding issue, even in the GOP primaries where the social conservatives are typically in control, maybe he's finally found an election cycle that plays to his sweet spot," said Boston University communications professor Tobe Berkovitz. "The planets are all lining up."
Still, Perry and Romney's other rivals portray him as a political chameleon - and probably will try again during Saturday night's debate in South Carolina.
Romney's history offers plenty of fodder, beginning with his gradual about-face on abortion.
During his first foray into politics - a failed 1994 campaign against incumbent Democratic Sen. Edward Kennedy - Romney said that while he was personally opposed to abortion, he believed the procedure "should be safe and legal."
Romney said his personal beliefs had no place in the race and his commitment to legal abortion stemmed from the death of a close relative during an illegal procedure.
Eight years later, as he was running for governor, Romney again pledged he would do nothing to change abortion rights laws in Massachusetts.
Then in 2005, after vetoing a bill that would have given rape victims access to emergency contraception at hospitals or through their pharmacists - a veto he said honored his pledge not to change the state's abortion laws - Romney declared himself "pro-life" in an editorial in the Boston Globe.
"I believe that abortion is the wrong choice except in cases of incest, rape, and to save the life of the mother," Romney wrote. "I wish the people of America agreed, and that the laws of our nation could reflect that view."
Romney has since said in a recent National Review editorial that he supports a reversal of Roe v. Wade, the landmark Supreme Court decision legalizing abortion, "because it is bad law and bad medicine."
Melissa Kogut, the former executive director of NARAL Pro-Choice Massachusetts, remembers meeting with Romney while he was still a candidate for governor. During the meeting, Kogut said Romney argued he could be a more moderate Republican voice on abortion.
"They know that this is killing them," Kogut recalls Romney saying of the political implications.
Kogut said she was surprised by Romney's shift.
"This is a man who had run for office before," Kogut said. "Clearly he had thought about it. It was a surprise to see him change so dramatically when he decided to run for president."
There were other shifts.
In 2005 Romney vetoed an embryonic stem cell research bill saying the research "crosses the boundary of ethics." Romney, whose wife, Ann, has multiple sclerosis, had previously voiced support for stem cell research, which advocates say holds the promise of treatment for a range of debilitating physical conditions.
Romney said his position evolved as he began to better understand the implications of embryonic stem cell research.
"It is wrong to allow science to take an assembly line approach to the production of human embryos, the creation of which will be rooted in experimentation and destruction," Romney said in a 2005 letter to lawmakers explaining his veto.
The Democrat-controlled Massachusetts Legislature quickly overturned the veto.
While Romney has found himself under fire from conservatives in his own party, others say they take his political evolution at face value.
Kristian Mineau, president of the Massachusetts Family Institute, which opposes gay marriage and abortion, called Romney "a great champion." Mineau said he believed that it was during the stem cell debate that Romney began to seriously examine some of his core values.
"I believe it was a genuine change of heart," Mineau said. "We have to give the governor the benefit of the doubt, and he has never wavered since."
Of all his past and present positions that Romney has tried to square, the most public has been his decision to sign Massachusetts' 2006 landmark health care overhaul - a sweeping law that provided a blueprint for Obama's health care law, the same law Romney has vowed to dismantle.
Ironically the "Romneycare" vs. "Obamacare" debate has also provided Romney with his most succinct retort. Romney has said the issues of health care should be left to the states, not the federal government.
It's a response that allows him to both defend his signature policy as governor while calling for the undoing of a very similar federal policy.
And on the question of gay rights and same-sex marriage, Romney has repeatedly pointed out that he never endorsed gay marriage, even during his 2002 campaign for governor.
Boston College political science professor Marc Landy said Romney's political contortions are inevitable given his electoral history.
To position himself for a run for president, Romney first chose to run for governor in one of the most liberal states in the nation. That forced him to adopt positions in keeping with Massachusetts' tradition of elected Republicans who are fiscally conservative but socially moderate.
Many of those social positions were inherently viewed as too liberal once Romney waded into the far more conservative GOP presidential waters - a gulf that was all too apparent as Romney awkwardly tacked to the right during his 2008 run for the nomination.
"I think he was really buffaloed by his strategy," Landy said. "He did this very ham-handed move to the right. It was dreadful to watch ... it made him look like the worst kind of hypocrite."