Lawyers for Gov. Corbett, whose administration had defended the state's law, said they were reviewing the decision. They have 30 days to appeal.
Across the state, elated couples and advocates celebrated a victory that some once believed they would never see. By midday Tuesday, gay and lesbian couples were rushing to Philadelphia City Hall to get a marriage license.
"I can't express how excited I am," said Christine Donato, a Delaware County woman and one of the plaintiffs in the case. Donato and her partner of 18 years, Sandy Ferlanie, have a 5-year-old son, Henry.
"Today, we get to say, 'Henry, you and your family are just as important and just as valued as any other couple and any other family in Pennsylvania,' " she said.
Another plaintiff, David Palmer of Northampton County, who has been with his partner, Ed Hill, for almost 25 years, put it this way: "Now, in our home, we are married."
Philadelphia Register of Wills Ronald R. Donatucci's office immediately began issuing marriage licenses to same-sex couples. Guy Sabelli, the city's marriage-license supervisor, said 18 same-sex couples obtained licenses by the time the office closed at 5:30 p.m.
In the 10 months since the U.S. Supreme Court struck down parts of the federal Defense of Marriage Act and the Pennsylvania lawsuit was filed, marriage bans have fallen in many states across the nation. Other battles continue.
On Tuesday, an appeals court in Idaho stayed a May 13 decision overturning a same-sex marriage ban there while Idaho's governor appeals.
How Corbett responds could be a defining decision for the Republican governor, who opposes gay and lesbian marriages and faces a tough reelection battle. Supporters of the ban faulted Jones' decision and urged an appeal.
Rob Gleason, chairman of Pennsylvania's Republican Party, said: "An activist judiciary has substituted its judgment in place of the law created by the elected representatives of Pennsylvania."
Added Randall Wenger, chief counsel for the Pennsylvania Family Institute: "We all want a more civil and loving society, but we don't achieve that by forcing a new definition of marriage through the courts."
Archbishop Charles J. Chaput, the leader of Philadelphia's Catholic archdiocese, called the decision "a mistake with long-term, negative consequences."
"Marriage is more than a private arrangement between two people," he said in a statement. "It's a public commitment of love and fidelity, and it's ordered not just to companionship, but to creating and rearing new life."
The lawsuit, Whitewood v. Wolf, was filed by 23 plaintiffs who said Pennsylvania's law violated the U.S. Constitution by excluding same-sex couples from the same legal benefits and protections as heterosexual couples.
A trial was initially expected this summer. But lawyers on both sides of the case told Jones that the evidence and testimony would not expand beyond what they had already presented in arguments and filings, setting the stage for a quicker decision.
"The issue we resolve today is a divisive one," Jones wrote in a 39-page opinion that invoked major civil rights cases of the past. "Some of our citizens are made deeply uncomfortable by the notion of same-sex marriage. However, that same-sex marriage causes discomfort in some does not make its prohibition constitutional. Nor can past tradition trump the bedrock constitutional guarantees of due process and equal protection."
Jones, 58, a Republican appointed in 2002 by President George W. Bush, noted that many of the plaintiffs were "spouses in every sense" and used the words traditionally found in wedding vows - "in sickness and in health," "til death do us part" - to describe their stories.
Mark Aronchick, one of the plaintiffs' lawyers in the case, called the judge brilliant and said his opinion was "one of the strongest" on the issue written in the United States.
The decision noted that "these are the vows that we make to each other in our society," Aronchick said. "If you look at what these people want, who they are - if you actually look into their hearts - they want to marry for the same reasons [as others], they have the same hopes, the same dreams."
The plaintiffs claimed that Pennsylvania's law, with its refusal to marry same-sex couples or recognize such marriages from other states, violated a fundamental right to marry, as well as the Constitution's equal-protection clause. The law not only bans same-sex marriage, but it also specifies that the state cannot honor such marriages from other states.
The suit contended that Pennsylvania had no legitimate interest in banning same-sex marriage, and that the ban disparaged and injured lesbian and gay couples and their families by denying them a long list of legal and financial protections afforded to heterosexual couples.
Witold "Vic" Walczak, legal director of the American Civil Liberties Union of Pennsylvania, which helped bring the case, said Jones' decision reinforced the position that Pennsylvania has effectively excluded "loving, committed couples" from the institution of marriage.
"Judge Jones could not have said that more emphatically," Walczak said.
At least six other cases are under consideration by courts in Pennsylvania, even as opinion polls show that a majority of voters favor allowing same-sex couples to marry.
The state Supreme Court is considering an appeal by Montgomery County Register of Wills L. Bruce Hanes of a lower-court decision barring him from issuing licenses to same-sex couples.
Should Jones' ruling stand up to appeal, it would render moot a lawsuit heard in Philadelphia last week, seeking to strike down the portion of Pennsylvania's law barring recognition of out-of-state same-sex unions. That case was brought by Isabelle Barker and Cara Palladino, who wed in Massachusetts and sued to have their marriage recognized in Pennsylvania.
But the couple said Tuesday that it hardly mattered to them whether it was their suit or another that accomplished their goals. They celebrated with a champagne toast in their offices at Bryn Mawr College, where both women work.
"There are a lot of people who worked on this issue to make this day come," Palladino said. "It's a great day for all Pennsylvanians. It's a great day for justice and equality in Pennsylvania, now that we've cracked the Liberty Bell."
Contributing to this article were Inquirer staff writers Jeremy Roebuck, Jessica Parks, Jason Grant, and Bob Warner.