In their decision, the panel of judges stated that the federal law banning same sex marriage was constitutionally flawed because it blocks states from defining marriage in a different way than the federal government.
Speaking with reporters in, McCaskill, who, has said in the past that she believes marriage is defined as between a man and a woman, said she agrees with the court's ruling that the issue is one of states' rights
"The way it has been crafted is one that I think most Missourians agree with the principles of limited government and states' rights," McCaskill said. "I think maybe on this particular subject, they want the Defense of Marriage Act, but I for one think it is much better for these decisions to be made at the state level like we have here in Missouri."
McCaskill added that she thinks "it will be interesting to see how this states' rights decision is handled by the Supreme Court because I think they are anxious to talk about a limited intervention with states rights when it suits their ideology."
One of McCaskill's leading Republican rivals, John Brunner, said Friday that he was "deeply disappointed" with the court's decision.
"Marriage is one of America's most sacred institutions and must be fiercely defended from activist courts and judges trying to legislate from the bench," he said in a statement.
The issue is now expected to head to the U.S. Supreme Court, where the court's conservative majority will decide on the law's constitutionality.