"The Constitutional Court nullified with a decision on December 4th, 2017 the legal regulation that until now prevented such couples from marrying," a statement said.
It said that this would come into force on December 31, 2018. The ruling came after a case was brought by two women in a registered civil partnership who were denied the right to marry by authorities in the capital Vienna.
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In April 2001 the Netherlands became the first country in the world to allow gay and lesbian couples to marry in a civil ceremony.
More than a dozen European countries have followed including most recently Germany. But others only allow same-sex couples to enter into civil partnerships.
Many eastern European countries -- including Bulgaria, Latvia, Lithuania, Poland, Romania and Slovakia -- deny homosexuals the right to marry or enter into unions.