The Mariners and Athletics will square off at the Tokyo Dome March 28-29.
It will be the fourth time Major League Baseball has opened a season with games in Japan. The New York Mets and Chicago Cubs played there in 2000, followed by the New York Yankees and Tampa Bay in 2004, and Boston and Oakland in 2008.
"Major League Baseball is very pleased to give Japanese fans a chance to see the Seattle Mariners and the Oakland Athletics, two franchises with great popularity in Japan," Selig said in a statement. "Opening Series 2012 will be an excellent opportunity to bring the game of baseball to fans across the globe and to celebrate the many contributions to the game by Japanese players. Most importantly, with the shared love of baseball between our nations, I believe that we can use this event to further assist the ongoing relief efforts throughout Japan."
The two big league teams also will play exhibition games against Japanese teams.
While Oakland and Seattle will return to the United States to wrap up exhibition play, the two games in Japan will count as regular-season games.
It means the two clubs won't play games that had been scheduled April 8 and July 5 in Oakland.
The Athletics and Mariners had been slated to play in Japan in 2003 but the trip was called off after the United States went to war in Iraq.