According to ESPN's Jesse Rogers, the Cubs announced the acquisition of Martin for a player to be named later and cash.
Martin will be eligible for the Cubs' postseason roster since he was acquired by the team prior to Sept. 1.
After playing in 143 games for the Mariners in 2016, Martin has been limited to 34 games this season. He was designated for assignment on Apr. 23 and was assigned to Triple-A before being recalled on July 30.
The Mariners designated Martin for assignment again on Aug. 23. The 29-year-old has hit just .174/.221/.287 in 115 at-bats this season. His outfield defense remains strong, with FanGraphs crediting him with five defensive runs saved in 262.1 innings played.
The Cubs currently have Jon Jay and Albert Almora splitting time in center field. Martin could be used in September when rosters expand to 40 players, giving him an opportunity to prove his value for a potential playoff push.