House and Senate Democrats who backed the bill as well as lesser-known people whose health care struggles have touched Obama were expected to join him Tuesday for the ceremony in the East Room. Afterward, Obama and much of that audience were heading to the Interior Department for an even larger celebration.
Act II begins Thursday when Obama visits Iowa City, Iowa, where as a presidential candidate he announced his health care plan in May 2007, to talk about how it will help lower health care costs for small businesses and families.
The House late Sunday voted 219-212 - no Republicans voted in favor - to send the 10-year, $938 billion bill to Obama. The measure, which the Senate passed in December, eventually will extend coverage to 32 million uninsured Americans, reduce federal budget deficits and ban such insurance company practices as denying coverage to people with existing medical problems.
A companion measure sought by House Democrats to make a series of changes to the main bill was approved 220-211. It goes to the Senate, where debate could begin as early as Tuesday. Majority Leader Harry Reid, D-Nev., says he has the votes to pass it - though only under special budget rules requiring just a simple majority vote.
Republicans united in opposition to Obama's redesign of the health care system, which they criticized as an unwarranted government takeover and pledged to repeal it. They plan to offer scores of amendments to slow or change the companion measure, which Democrats hope to approve as written and send directly to Obama for his signature.
Within six months of enactment of the bill - or by the end of September - consumers should notice some changes. Among them, insurers would be required to keep young adults as beneficiaries on their parents' health plans until they turn 26, and companies would no longer be allowed to deny coverage to sick children.
Other changes would not kick in until 2014.
By then, most Americans will for the first time be required to carry health insurance - either through an employer, through a government program or by buying it for themselves. Those who refuse will face penalties from the IRS.
Tax credits to help pay for premiums also will start flowing to middle-class working families with incomes up to $88,000 a year, and Medicaid will be expanded to cover more low-income people.
The nonpartisan Congressional Budget Office said the bill awaiting Obama's signature would cut federal budget deficits by an estimated $143 billion over a decade.
The second measure, which House Democrats demanded before agreeing to approve the first one, includes enough money to close a gap in Medicare prescription drug coverage over the next decade, starting with an election-year rebate of $250 later this year for seniors facing high costs.
Polls show the public is split over the bill, so Obama will stick with the sales job for the foreseeable future, with an eye toward helping those Democrats who cast risky votes for his plan and who are facing tough re-election battles in November.