In its decision, the court upheld a 2007 district court judge's ruling that the law violates the state constitution. It strikes the language from Iowa code limiting marriage to only between a man a woman.

"The court reaffirmed that a statute inconsistent with the Iowa constitution must be declared void even though it may be supported by strong and deep-seated traditional beliefs and popular opinion," said a summary of the ruling issued by the court.

The ruling set off celebration among the state's gay-marriage proponents.

"Iowa is about justice, and that's what happened here today," said Laura Fefchak, who was hosting a verdict party in the Des Moines suburb of Urbandale with partner of 13 years, Nancy Robinson.