Seager spent the entire 2010 season with the High Desert Mavericks, batting .345 with 14 home runs and 74 RBIs.

On June 5, 2013, Seager hit a grand slam against the Chicago White Sox in the 14th inning.

It was the first time in MLB history that a player hit a game-tying grand slam in extra innings.

The first walk-off hit of his career, his performance earned him an April Co-Player of the Week Award, shared with José Abreu of the White Sox.

The first Mariner to accomplish the feat, he became the first MLB player with two triples and at least one double and homer in a game since Hal Breeden for the Montreal Expos in 1973.

On July 7, he was named to his first All-Star team as an injury replacement for Toronto Blue Jays player Edwin Encarnación.

[16] He finished the 2014 season with a .268 batting average, 25 home runs and 96 RBIs in 159 games, and won a Gold Glove award.

In 2019, during a spring training game, Seager sustained an injury to his left hand while attempting a diving play on a ball.

[27] In 2020, Seager batted .241/.355/.433 with nine home runs and 40 RBIs and led the AL with 6 sacrifice flies.

[1][29] Knowing back in spring training that the Mariners were likely not going to pick up the option, Seager went into the 2021 season expecting it to be his last one.

[30] During the following off-season, the Texas Rangers inquired if Seager would be interested in coming out of retirement to join up with his brother, Corey, who had signed with the team a few months earlier.