The series will mark the eighth season-opener to be played internationally and first in Japan since 2012 when the A's and Mariners split the two games, MLB said in a statement.
Oakland and Seattle will contest their series at the Tokyo Dome on March 20-21 after competing against Nippon Professional Baseball (NPB) teams in day/night doubleheaders earlier that week against opponents to be determined at a later date.
MLB has previously opened seasons in Monterrey, Mexico (1999); Tokyo (2000, 2004, 2008, 2012); San Juan, Puerto Rico (2001); and Sydney, Australia (2014).
MLB also announced an All-Star tour of Japan from Nov. 8-15 2018 that will consist of four games in Tokyo followed by one at Hiroshima and two in Nagoya.
The opening game of this year's tour will be versus the Yomiuri Giants while the remaining games will be against a Japanese All-Star team.
Nippon Professional Baseball Commissioner Atsushi Saito said: "With our (Japan's) goal of winning a gold medal in the 2020 Olympic Games in Tokyo, this gives our players experience in high-level games against MLB players".
(Reporting by Frank Pingue in Toronto; Editing by Ken Ferris)