WASHINGTON — President Obama signed his first bill into law on Thursday, approving equal-pay legislation that he said would “send a clear message that making our economy work means making sure it works for everybody.”

Mr. Obama was surrounded by a group of beaming lawmakers, most but not all of them Democrats, in the East Room of the White House as he affixed his signature to the Lilly Ledbetter Fair Pay Act, a law named for an Alabama woman who at the end of a 19-year career as a supervisor in a tire factory complained that she had been paid less than men.

After a Supreme Court ruling against her, Congress approved the legislation that expands workers’ rights to sue in this kind of case, relaxing the statute of limitations.

“It is fitting that with the very first bill I sign — the Lilly Ledbetter Fair Pay Act — we are upholding one of this nation’s first principles: that we are all created equal and each deserve a chance to pursue our own version of happiness,” the president said.

He said was signing the bill not only in honor of Ms. Ledbetter — who stood behind him, shaking her head and clasping her hands in seeming disbelief — but in honor of his own grandmother, “who worked in a bank all her life, and even after she hit that glass ceiling, kept getting up again” and for his daughters, “because I want them to grow up in a nation that values their contributions, where there are no limits to their dreams.”

The ceremony, and a reception afterward in the State Dining Room of the White House, had a celebratory feel. The East Room was packed with advocates for civil rights and workers rights; the legislators, who included House and Senate leaders and two moderate Republicans — Senators Susan Collins and Olympia Snowe, both of Maine — shook Mr. Obama’s hand effusively (some, including House Speaker Nancy Pelosi, received presidential pecks on the cheek) as he took the stage. They looked over his shoulder, practically glowing, as Mr. Obama signed his name to the bill, using one pen for each letter.

“I’ve been practicing signing my name very slowly,” Mr. Obama said wryly, looking at a bank of pens before him. He handed the first pen to the bill’s chief sponsor, Senator Barbara Mikulski, Democrat of Maryland, and the last to Ms. Ledbetter.

The ceremony also marked First Lady Michelle Obama’s policy debut; she spoke afterward in a reception in the State Dining Room, where she called Ms. Ledbetter “one of my favorite people.”

Mr. Obama told Ms. Ledbetter’s story over and over again during his campaign for the White House; she spoke frequently as an advocate for him during his campaign, and made an appearance at the Democratic National Convention in Denver.

Now 70, Ms. Ledbetter discovered when she was nearing retirement that her male colleagues were earning much more than she was. A jury found her employer, the Goodyear Tire and Rubber Company plant in Gadsden, Ala., guilty of pay discrimination. But in a 5-4 decision, the Supreme Court threw out the case, ruling that she should have filed her suit within 180 days of the date that Goodyear first paid her less than her peers.

Congress tried to pass a law that would have effectively overturned the decision while President George W. Bush was still in office, but the White House opposed the bill; opponents contended it would encourage lawsuits and argued that employees could delay filing their claims in the hope of reaping bigger rewards. But the new Congress passed the bill, which restarts the six-month clock every time the worker receives a paycheck .

Ms. Ledbetter will not see any money as a result of the legislation Mr. Obama signed into law. But what she has gotten, aside from celebrity, is personal satisfaction, as she said in the State Dining Room after the signing ceremony.

“Goodyear will never have to pay me what it cheated me out of,” she said. “In fact, I will never see a cent. But with the president’s signature today I have an even richer reward.”