Major League Baseball said Thursday the change was made because of the scheduling conflict at Sun Life Stadium. The rock band U2 is scheduled to play at the stadium June 29 and the Marlins must vacate the stadium to allow setup time for the concert.
Marlins president David Samson told MLB.com that the team was anticipating the series would be moved and invoiced the Marlins' season-ticket holders for only 78 games this season.
"What happened was U2 had to reschedule for a year later, and the baseball schedule was such that there was no other way to have us at home that series," Samson told MLB.com. "We obviously couldn't play at home, because we don't control the stadium. For one final season, we are tenants.
"So we worked closely with baseball for an alternate venue. The best and only solution was to play the games in Seattle."
The Marlins are scheduled to move to a retractable-roof stadium in 2012 and will change their name to the Miami Marlins next season.
Florida will remain the home team and will bat last, and the series will be played under NL rules, without a designated hitter.
Information from The Associated Press was used in this report.