Attorneys for the city had asked the high court to overturn a lower court ruling that the gun ban violated state law. But the Supreme Court justices declined to even look at the case, reaffirming that the gun ban is illegal.
The National Rifle Association cheered the ruling, saying that it represents a "final victory" for Seattle gun owners.
"The Washington Supreme Court made the right decision in recognizing that the city violated state law," said Chris W. Cox, executive director of the NRA's Institute for Legislative Action.
But Seattle City Attorney Pete Holmes said the city should be allowed to set policy on property it owns, including a gun ban, to protect the safety of park users.
"They would like to know that no one should have the right to arm themselves in the park that they're sharing with families," he said.
The case began in 2008, when the city of Seattle and then-Mayor Greg Nickels enacted a rule that banned firearms from city parks, community centers and other city properties. That rule was prompted in part by a shooting at the 2008 Northwest Folklife Festival in Seattle that injured two bystanders.
In 2009, the city added another rule that banned guns from parks where children were likely to be present.
In October 2009, the NRA and the Second Amendment Foundation asked a King County Superior Court judge to strike down the rules as a violation of a state law prohibiting localities from enacting this type of ban on guns.
In response, the city replied that the ban was permissible because it was acting in its interest as owner of the park properties.
In 2010, a King County Superior Court judge struck down the gun ban, and the state Court of Appeals later confirmed that ruling. By declining to review the appeals court ruling, the state Supreme Court reaffirmed it, and the gun ban is now history.
But Holmes said the city of Seattle hopes to pursue the issue in the next legislative session, by pushing for a change in the state law that prohibits city gun bans.