The presidential nominees never crossed paths, and partisanship was largely out of view during the back-to-back appearances before thousands of the Clinton group's members.
Romney largely muted his sharp criticism of Obama's foreign policies, specifically of the president's response to the violent anti-American protests sweeping the Middle East this month.
He got in one jab, saying, "I will never apologize for America." Romney has frequently said that Obama has offered apologies to foreign governments, a contention disputed by independent fact-checkers.
After Clinton delivered a warm introduction of the Republican, Romney announced his proposal for a "Prosperity Pact," which he said would link trade policy with development policy to promote investment and entrepreneurship in developing nations.
"Nothing we can do as a nation will change lives and nations more effectively and permanently than sharing the insight that lies at the foundation of America's own economy, and that is that free people pursuing happiness in their own ways build a strong and prosperous nation," Romney said in his 17-minute speech.
Romney's foreign-aid plan, which he called "a new approach for a new era," echoes the domestic policy themes of his presidential campaign. Under his plan, the government's foreign aid would be more closely linked to trade policies as well as private investment and corporate partnerships. He said this could "empower individuals, encourage innovators, and reward entrepreneurs."
For example, Romney would support new financing structures for small- and medium-size enterprises that are too large to benefit from microfinance programs but too small to acquire capital from banks.
He stopped short of criticizing U.S. foreign-assistance programs or saying he would cut foreign-aid budgets, as many Republican leaders have done. But Romney did contend that foreign-aid programs focus too much on delivering social services instead of seeding longer-term reforms.
"A temporary aid package can give an economy a boost," Romney said. "It can fund some projects. It can pay some bills. It can employ some people some of the time. But it can't sustain an economy, not for the long term. It can't pull the whole cart, if you will, because at some point the money runs out. But an assistance program that helps unleash free enterprise creates enduring prosperity."
Later, Obama gave an impassioned speech against human trafficking, noting that some girls sold off by poor families are no older than his two daughters.
"I've made it clear that the United States will be a leader in this global movement against trafficking," Obama said, adding that his administration is helping other countries meet international goals designed to reduce trafficking.
He said the United States must stop the human trafficking within its boundaries, which mostly affects immigrant communities who are sometimes more vulnerable because of their members' undocumented status and poverty.
"We cannot ask other nations to do what we are not doing ourselves," he said. Obama said he signed an executive order to better ensure that U.S. tax dollars never go to companies or groups that conduct human trafficking.
The gathering was nonpartisan, but Romney did make one reference to the state of the presidential campaign.
After Clinton walked offstage, Romney suggested that the former president was responsible for Obama's polling lead.
"If there's one thing we've learned in this election season, by the way, it's that a few words from Bill Clinton can do a man a lot of good," Romney said, drawing laughter from the audience. "All I've got to do now is wait a couple of days for that bounce."
Later Tuesday, Romney made the first of his four planned Ohio stops this week, joining his running mate, Rep. Paul Ryan, for a rally near Dayton.
On Wednesday, Obama will visit the college towns of Kent and Bowling Green, and Romney's bus tour will stop in the Columbus, Cleveland, and Toledo areas.
This article contains information from the Associated Press.