Justin Smoak and Logan Morrison have split time at first base this season for Seattle, and both have struggled to produce. Morrison is batting .211 this year, and Smoak was sent to Triple-A Tacoma on Monday after batting .208 in 69 games.
Morales signed with the Twins in June and has batted .234 in 39 games thus far this season.
Morales spent the 2013 season with the Mariners and batted .277 with a .449 slugging percentage.
Seattle sent minor-league pitcher Stephen Pryor to Minnesota in the trade. Pryor played for both Double A Jackson and Triple A Tacoma this season, posting a 4.65 ERA.
The Mariners currently sit a half game ahead of the Yankees and Blue Jays for the American League's final wild card spot.
- Dan Gartland