A federal judge in san antonio made that ruling wednesday.
However, the state's ban will remain in place pending appeals to higher courts.
This case is expected to eventually make it's way to the U.S. Supreme Court.
Civil rights leaders have said all along the ruling was inevitable.
Judge Orlando Garcia struck down the 2005 amendment to the state constitution that was approved by voters.
In his ruling, judge Garcia said.... "these Texas laws deny plaintiffs access to the institution of marriage and its numerous rights for the sole reason that they wish to be married to a person of the same sex.
The judge however said he would not enforce his ruling until the 10th circuit court of appeals weighs-in.
Texas Attorney General Greg Abbott plans to file an expedited appeal.
17 states and the District of Columbia currently allow same sex marriage.
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