Romney, whose family has belonged to the LDS faith for generations, appears to have donated about 10 percent of his income to his church, meeting the "tithing" requirement for devout Mormons.
"Elections should be determined by more than what your tax return looks like," says Rep. Jason Chaffetz, R-Utah and a Romney supporter, "but he should get some brownie points for being so generous."
Romney's philanthropic donations top that of most politicians who have released their taxes including President Barack Obama, whose last return showed charitable contributions of $245,000, or about 14 percent of the income between him and his wife, Michelle.
Vice President Joe Biden and his wife, Jill, donated about $5,000 to charity in 2010. Romney's chief GOP challenger, former House Speaker Newt Gingrich, gave about 2.6 percent of his income in 2010 to charity.
Of course, Obama, Biden and Gingrich paid higher rates of income taxes than Romney did, a point critics seized upon Tuesday.
Romney paid $6.2 million in taxes over the two-year period, with an effective tax rate of 13.9 percent. The wealthiest candidate in the presidential chase, Romney's net worth ranges from $190 million to $250 million, according to campaign aides and personal financial disclosures.
The release of his tax returns coming after months of prodding by Democrats, rival Republicans and news media pundits could pose an obstacle for Romney, who is trying to avoid being labeled as out of touch with average Americans.
Romney's return, for example, listed a Swiss bank account and investments in the Cayman Islands, a tax haven. His advisers noted that the former Massachusetts governor paid taxes on those investments.
Brad Malt, who handled the Romneys' blind trusts, said he closed the Swiss account because "it wasn't worth it" and that it might not be consistent with Romney's political views.
The one-time GOP front-runner "will have a very difficult time getting any other message out, except for debating his taxes," Eddie Mahe, a Republican consultant who hasn't endorsed a candidate, told Bloomberg News. "It is unbelievable they could allow themselves to get into that situation. That's not what you want to be talking about."
Patrick Gaspard, the Democratic National Committee's executive director, noted that Romney has opposed the so-called Buffet Rule, which would increase the rate at which investment income is taxed to match that of earned income.
"Now we know why [he opposes that increase]," Gaspard said. "Mitt Romney pays a lower tax rate than most police and firefighters, teachers and small-business owners, and he doesn't want that to change."
Romney tackled that accusation during the NBC debate in Florida on Monday night, noting that he pays his taxes that are "legally required and not a dollar more."
"I don't think you want someone as the candidate for president," he said, "who pays more taxes than he owes."
Of course, Romney's tax rate was lower partly because of deductions from hefty charitable giving.
Ben Ginsberg, Romney's longtime attorney, highlighted the millions in donations, adding that the sizable donations to the LDS Church reflect his "lifelong commitment" to his faith.
Romney and his wife also donate to charity and their church through the Tyler Charitable Foundation.
Since 2000, the foundation has donated about $4.8 million to the LDS Church, according to the charity's financial information, and about $525,000 to Romney's alma mater, church-owned Brigham Young University.
Una Osili, the director of research at the Center on Philanthropy at Indiana University, said a recent study by her group shows that wealthy Americans on average donated about 11 percent of their income in 2007 but that dropped to 9.1 percent in 2009, the most recent year in which figures were available. Average U.S. households, she added, give about 1 percent or 2 percent of their income to charity.
Osili also noted that studies by the center have shown that regular worshippers, such as Romney, typically give more to charity than those who do not.
Romney's 2011 tax return appears below. View all the 2010 tax documents at http://mittromney.com/learn/mitt/tax-return/main
Mitt Romney 2011 Tax Return
• 2011 embedded in this story
• 2010 returns at http://mi.tt/xETEtU