Jackson, 28, was acquired by the Mariners on July 31, 2014, from the Tigers. He'll be a free agent at the end of this season.
The Texas native put up a .272/.312/.387 line this season with eight homers, 38 RBIs and 15 stolen bases in 107 games. He batted .394 over his last 18 games, with five doubles, a triple and two homers.
"I got a chance to be around a lot of good players, a lot of veteran guys that have done well," Jackson said of his year with the Mariners. "I'm talking about [Nelson Cruz] a lot, because he's just one of those players that makes you a better player. [Robinson Cano], being able to pick his brain a little bit. Playing behind [Felix Hernandez], those are things you can put in your memory bank and store them for another day, maybe for the grandkids or something like that. There've been some pretty good moments here."
Jackson is a six-year Major League veteran who spent his first four and a half seasons with the Tigers and was part of three postseason clubs. He's a career .273 hitter with a .733 OPS in 831 games and is a solid defensive center fielder.
Jackson acknowledged disappointment in how the Mariners' season played out, but said he's looking forward to joining a young, contending team in the Cubs and seeing how he can help out.
"We definitely came in with high expectations," Jackson said about the 2015 season for Seattle. "We didn't fulfill those. It's just baseball. You are frustrated by it, but this is a business, and you understand that part of it."
The Mariners will now give Miller more time in center field as he transitions from a shortstop role. Miller has started eight games in left field, three in center and one in right this season, and was back in center again in Monday's series opener against the Astros after initially being penciled in at shortstop prior to Jackson's trade.
"We'd like to see quite a bit of that," Kingston said. "I just spoke to [manager Lloyd McClendon] about it. I think at this point, that's probably [Miller's] best fit for this organization going forward. We think he has the components and skill set to play out there, and if he can, it's a huge asset to this organization."
Ketel Marte, 21, has played well at shortstop since being called up from Tacoma a month ago and likely will get the bulk of playing time there down the stretch.