The decision came two years after the high court overturned the state's own ban on gay marriage, Proposition 8. Harris had refused to defend the ban, calling it unconstitutional.
"California is validated. We are validated," she said during a news conference at her office in Sacramento.
Harris called on individual states to quickly begin implementing the court's decision.
"Each day that one of those couples have to go without being able to have their marriage and their love legally recognized ... is one day too long," she said.
Harris also had a message for Supreme Court Justice Antonin Scalia, who dissented from the decision and singled out California as a cultural outlier.
"Don't hate the playa, hate the game," she said.
Harris added, "Justice Scalia has caused many people to question the dignity of the court when he makes statements such as the statements he’s made in connection with this case. And that’s unfortunate."
Harris said she plans to spend the weekend in San Francisco, celebrating pride weekend with her husband.
Follow @chrismegerian for more updates from Sacramento.