On December 13, 2013, the Marlins traded Morrison to the Seattle Mariners for pitcher Carter Capps.
He reverted to wearing number 20 during his tenure with the Mariners.
Morrison played in just eight games before sustaining a hamstring injury, causing him to miss nearly two months of the season.
On June 11, he was activated from the disabled list, and immediately took over the first base role vacated by Justin Smoak, who went down with an injury.
In 99 games in 2014, Morrison hit .262/.315/.420 while finishing with 11 home runs and 38 RBIs in 336 at bats.
Over the final two months of the season (49 games), he hit .321/.375/.512 with 6 home runs and 20 RBIs, solidifying his role as the Mariners' first baseman heading into 2015.
Smoak was allowed to leave the club via waivers, and Morrison avoided arbitration with Seattle for $2.725 million.

Morrison appeared in 146 games and 457 at bats for Seattle in 2015, with 115 starts at first base.
He hit .225/.302/.383 with 17 home runs and 54 RBIs, with a wRC+ of 90, a significant dropoff from his 2014 value of 111.
His fielding percentage of .996 was identical from 2014 to 2015, but his Defensive Runs Saved total of -7 was worse in 2015 than his 0 total in 2014.
Morrison also struggled against left-handed pitchers in 2015, hitting .190 with a 19.4% strikeout rate, higher than his season total of 15.9%
On December 13, 2013, the Marlins traded Morrison to the Seattle Mariners for pitcher Carter Capps. He reverted to wearing number 20 during his tenure with the Mariners. Morrison played in just eight games before sustaining a hamstring injury, causing him to miss nearly two months of the season. On June 11, he was activated from the disabled list, and immediately took over the first base role vacated by Justin Smoak, who went down with an injury. In 99 games in 2014, Morrison hit .262/.315/.420 while finishing with 11 home runs and 38 RBIs in 336 at bats. Over the final two months of the season (49 games), he hit .321/.375/.512 with 6 home runs and 20 RBIs, solidifying his role as the Mariners' first baseman heading into 2015. Smoak was allowed to leave the club via waivers, and Morrison avoided arbitration with Seattle for $2.725 million.
Morrison appeared in 146 games and 457 at bats for Seattle in 2015, with 115 starts at first base. He hit .225/.302/.383 with 17 home runs and 54 RBIs, with a wRC+ of 90, a significant dropoff from his 2014 value of 111. His fielding percentage of .996 was identical from 2014 to 2015, but his Defensive Runs Saved total of -7 was worse in 2015 than his 0 total in 2014. Morrison also struggled against left-handed pitchers in 2015, hitting .190 with a 19.4% strikeout rate, higher than his season total of 15.9%
Logan Morrison