In June, Clinton and Obama appeared together in Unity, N.H., in a symbolic event to push for party unity after their long and often bitter primary battle. Both also have been helping each other raise money, in Clinton's case to retire her own hefty campaign debt.
The announcement came a day after former President Clinton defended his role in the hard-fought Democratic primary. He said that while he may have some regrets, he was not a racist and had never attacked Obama personally.
"There are things that I wish I'd urged her to do. Things I wish I'd said. Things I wish I hadn't said," the former president told ABC News.
Democrats hope the Clintons and Obama can persuade supporters on both sides to put aside any bad feelings and come together to defeat Republican Sen. John McCain this fall.
Sen. Clinton is scheduled to deliver a speech at the Democratic National Convention in Denver later this month, but her husband's role there is still unclear.
Sen. Clinton conceded to Obama in early June after the primaries ended and he'd locked up sufficient convention delegates to win nomination.
Since then, she has been slowly re-injecting herself into the New York political scene from which she's been largely absent for more than a year. On Monday night, she was the guest of honor at a party thrown by Mayor Michael Bloomberg.
At the party, Clinton thanked constituents for putting their demands on hold for 18 months while she campaigned for president. "Now the hold is off, and I am open for business, 100 percent of the time and really looking forward to working with you on behalf of this city and state that we love," Clinton said.
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Associated Press writer Sara Kugler in New York contributed to this report.
