Judge Terry Lewis on Thursday found that the state's Republican-controlled Legislature broke the law when it drew up political maps in 2012. He rejected arguments from top legislative leaders that they had done nothing wrong.
Lewis' ruling, however, is not expected to disrupt this year's elections because the Legislature is expected to appeal the decision.
A 12-day trial marked the first test of a 2010 constitutional amendment approved overwhelmingly by voters that said legislators could no longer draw up districts to favor incumbents or a political party.
A coalition of groups contended that legislators used a "shadow" process to conceal the role of GOP consultants who helped craft the final maps.