Seager, 27, set career highs by hitting .268 with 25 home runs and 96 RBI. He also won his first Gold Glove last season.
With the anticipated signing, Seager will join American League MVP Mike Trout, 2012 National League MVP Buster Posey and Atlanta Braves first baseman Freddie Freeman as only players to sign $100 million plus deals before or in their first season of salary arbitration.
Seager was the team's third-round pick out of North Carolina in 2009. He has 70 career home runs and 264 RBI in four seasons with the Seattle. The Mariners will now have three players who have nine-figure deals. Seager joins second baseman Robinson Cano and ace Felix Hernandez.
Seattle went 87-75 last season and finished third in the AL West. The Mariners have not been to the playoffs since 2001.
- Scooby Axson