A federal judge has declared Texas's ban on gay marriage unconstitutional but left it in place until an appeals court can rule on the case.
The ruling is the latest in a series of victories for gay-rights activists following similar decisions in Utah, Oklahoma and Virginia.
Judge Orlando Garcia issued the preliminary injunction after two gay couples challenged a state constitutional amendment and a longstanding law.
He said the couples were likely to win their case and the ban should be lifted, but said he would give the state time to appeal to the Fifth Circuit Court of Appeals before doing so.
"Without a rational relation to a legitimate governmental purpose,state-imposed inequality can find no refuge in our United States constitution,'' Garcia wrote.
"These Texas laws deny plaintiffs access to the institution of marriage and its numerous rights, privileges, and
responsibilities for the sole reason that plaintiffs wish to be married to a person of the same sex.''
Greg Abbott, Texas's attorney general, was expected to file an expedited appeal.
Mark Phariss and Victor Holmes filed their federal civil rights lawsuit saying Texas's ban unconstitutionally denied them the fundamental right to marry because of their sexual orientation.
Cleopatra De Leon and Nicole Dimetman filed a lawsuit saying Texas officials were violating their rights by not recognising their marriage conducted in a state where gay marriage is legal.
Attorneys for the state argued that Texas voters had imposed the ban through a referendum and that Texas officials were within their rights to defend marriage traditions.
Another gay couple filed a separate lawsuit in federal court in Austin. In that case, two men argued that the ban discriminated against them based on their gender. That case is scheduled for a hearing later this year.