The Mariners selected Washington's contract from High-A Everett on Tuesday, Ryan Divish of The Seattle Times reports.
With Randy Arozarena (hamstring) and Luke Raley (back) both sitting out Tuesday with injuries, the Mariners will promote Washington from High-A all the way to the majors to give depth to their outfield unit. The 26-year-old has slashed just .190/.280/.394 at Everett this season and is unlikely to play outside of an emergency.