So many gay rights and Democratic activists were expected at the signing ceremony that the White House booked a large auditorium at the Interior Department.
"This day has come!" said an elated Mike Almy, an Air Force major discharged four years ago when his sexual orientation became known. "'Don't ask, don't tell' is over, and you no longer have to sacrifice your integrity."
While the elation is real, Pentagon officials caution it could be premature, since the bill requires service chiefs to complete implementation plans before lifting the old policy - and certify to lawmakers that it won't damage combat readiness, as critics charge.
Also, guidelines must be finalized that cover a host of practical questions, from how to educate troops to how sexual orientation should be handled in making barracks assignments.
While officials have avoided timetables, the process will probably take months.
Still, for gay and lesbian Americans, Wednesday is a watershed. And for Mr. Obama, it is a day to revel in the achievement of a goal he's long championed.
It is also the second of three expected victories in what's turned out to be - for Mr. Obama - a surprisingly productive lame-duck Congress. Weeks after his self-described "shellacking" in the midterm vote, he's won lopsided approval of a tax cut compromise, and the Senate is poised to deliver his top foreign policy goal: ratification of a new nuclear arms treaty with Russia.
Many Democratic liberals were furious over the tax package, believing Mr. Obama blithely yielded to Republican demands to retain the same tax cuts for the rich he had loudly denounced on the campaign trail. That's not the case with the repeal of don't ask, don't tell. Lifting of the ban on gays serving openly was something Mr. Obama not only campaigned on in 2008 but reiterated in this year's State of the Union speech.
"I will work with Congress and our military to finally repeal the law that denies gay Americans the right to serve the country they love because of who they are," he said in January to cheers in the House chamber, adding, "It's the right thing to do."
Born 17 years ago as a compromise between President Bill Clinton and a resistant Pentagon, the "don't ask, don't tell" policy became for gay rights campaigners a notorious roadblock on the way to full acceptance.
Speaking in June at a Gay Pride Month observance at the White House, Mr. Obama likened the fight to end it to the struggle of American blacks for civil rights.
"We have never been closer to ending this discriminatory policy," he declared.
Yet he has also faced rising discontent among gay activists who believed he hadn't moved forcefully enough. He's been heckled at campaign appearances over AIDS funding and the failure to end the military service ban.
Mr. Obama countered that as commander-in-chief, he had to ensure the ban's end is carefully prepared for.
That's just what the bill from Congress mandates.
"The implementation and certification process will not happen immediately; it will take time," Air Force Chief of Staff Gen. Norton Schwartz warned in an e-mail that went out right after Saturday's Senate vote. "Meanwhile, the current law remains in effect. All Air Force members should conduct themselves accordingly."
Military and administration officials are wrestling with numerous legal questions raised by the end of the ban - knowing that courts are waiting in the wings. They include what to do about pending expulsion proceedings, and when those ousted under don't-ask-don't-tell might apply to rejoin the armed forces.
For Almy, who appeared at a Capitol Hill ceremony Monday, the important thing is that gay and lesbian service members are no longer singled out because of who they love.
"That's all we ever wanted," he told reporters, "not special rights, just the same as our straight counterparts."