In anticipation of the ruling, the Bella Vista couple kept their afternoon clear and made sure they were close to the office of Ronald R. Donatucci, whose office handles marriage licenses. Donatucci, the city's register of wills, said he agreed to personally pay Landau and Smith's $80 fee as part of a commitment he made to Mark Segal, publisher of the Philadelphia Gay News.
Segal was 10th in line for a license to marry his partner of 10 years, Jason Villemez.
All but two employees in Donatucci's office had taken the day off to perform political work for the primary election, but they were called back once the federal judge's decision became public.
By 5:30 p.m., when the office closed, 18 couples had been processed in the hours after the court ruling.
The office will reopen at 8 a.m. Wednesday and close at 7 p.m.
More than 300 jubilant gay-marriage supporters thronged a wide plaza outside City Hall from late Tuesday afternoon into the evening, chanting "Don't appeal," bobbing up and down to live music, and cheering a range of speakers as they reveled in the news.
Waving signs emblazoned with such slogans as "Love Wins! - Why Marriage Matters Pennsylvania," many in the crowd beamed, hugged one another, and talked excitedly about how their lives had just changed in an instant.
Landau said she received a phone call from a representative of Mayor Nutter, who asked to preside over their marriage ceremony, set for Tuesday.
"This has been a long road, and we knew Pennsylvania was going to be taking up the tail end, but we're so glad it happened when it did," Landau said.
"We've talked at times about getting married in other states," but chose to wait for Pennsylvania, she said.
"We have a 6-year-old son. He wants us to be married here," Landau said.
Landau and Smith were not involved in the lawsuit.
At 3:46 p.m., Nutter tweeted: "Congrats to all of the activists in the LGBT community and the supporters - marriage equality for all."
Philadelphia Archbishop Charles J. Chaput issued a statement shortly before 5 p.m. condemning the federal judge's decision.
"Today's federal District Court decision striking down Pennsylvania's Defense of Marriage Act is a mistake with long-term negative consequences," he said.
"Like many other Pennsylvanians, I hope that an appeal will be made promptly. Laws that defend the traditional definition of marriage were enacted for sound reasons - namely to defend the rights of children and contribute to the well-being of the larger community.
"Marriage is more than a private arrangement between two people. It's a public commitment of love and fidelity, and it's ordered not just to companionship but to creating and rearing new life. This is why every child deserves a mother and a father in a loving marriage, and the child is the fruit of that love," he said.
"All men and women are formed in the image of God and deserve our respect. But attempts to redefine the nature of marriage, no matter how well-intentioned, damage a cornerstone of our human interaction and ultimately work against human dignity itself."
Pennsylvania Republican Chairman Rob Gleason also decried the ruling.
"Today, an activist judiciary has substituted its judgment in place of the law created by the elected representatives of Pennsylvania and has stifled the ongoing debate of people with differing points of view," Gleason said.
A sampling of reaction in Center City to the court's ruling was favorable.
At 12th and South Streets, Robert Braun, 66, a semiretired business owner, welcomed it.
"It's about time that gay and lesbian people had the same civil rights, with respect to marriage, that straight people have," said Braun, who is not gay. "I have been sending congratulations to all of my gay friends."
Near Independence Hall, Courtney Foster, an 18-year-old sophomore at St. Joseph's University, smiled as she was told by a reporter that same-sex couples could now wed in Pennsylvania.
"I think it's about time," she said without missing a beat. "I think marriage should be available to anyone."
After pausing a moment, she added, "Their marriage doesn't harm anyone, just like if I got married, it wouldn't affect them."
A few yards away, her friend Alexis Thompson, 20, also was quick to support the ruling.
"I think it's good," said Thompson, a Nebraska native who said she was touring the city and visiting Foster. "I think everyone should have the opportunity to express who they love, and I think marriage is an important aspect of that."
Thompson also said that she agreed with the Pennsylvania federal judge's decision that the legal benefits of marriage should extend to same-sex couples.
Contributing to this article were Inquirer staff writers Robert Moran, Vernon Clark, and Troy Graham.