A federal judge struck down Indiana's ban against gay marriage on Wednesday.
U.S. District Judge Richard Young found the state's Defense of Marriage Act to be unconstitutional. The attorney general plans to appeal the ruling.
The law was enacted in 2004, and defined marriage in biblical terms – between a man and a woman. Judge Young said that that definition is a constitutional violation.
"Same-sex couples, who would otherwise qualify to marry in Indiana, have the right to marry in Indiana," he wrote in his decision. "These couples, when gender and sexual orientation are taken away, are in all respects like the family down the street. The Constitution demands that we treat them as such."
An hour after the ruling, marriage licenses were being issued in Marion County Clerk's office.
Lambda Legal, who defended five of the plaintiffs, applauded the decision.
"Indiana now joins the momentum for nationwide marriage equality and Hoosiers can now proclaim they are on the right side of history," they said in a statement.
The legislature is currently revising a proposed constitutional amendment banning gay marriage, but the measure, if passed, would not appear on a ballot until November 2016 at the earliest. It is unclear what effect Wednesday's ruling will have on these efforts.
In December, the state's Catholic bishops issued a statement affirming their stance on same-sex marriage.
"The Church upholds the dignity of every human person, including persons with same-sex attraction, who 'must be accepted with respect, compassion, and sensitivity,'" the statement read.
"At the same time, the Church upholds the dignity and sanctity of marriage, a natural institution established by God. By its very nature, marriage is a permanent partnership between one man and one woman ordered to the good of the couple and the procreation and education of children."
Each of the 31 states that had gay marriage bans have had their bans challenged in court. Dozens of lawsuits are pending across the nation.