The 1989 Seattle Mariners season was their 13th since the franchise creation. The team finished in sixth place in the American League West division, with a record of 73–89 (.451). The Mariners were led by first-year manager Jim Lefebvre.

The season was enlivened by the arrival of 19-year-old Ken Griffey Jr., the 1st overall pick of the 1987 Major League Baseball (MLB) draft. The team traded for fellow future Hall of Famer Randy Johnson in May, sending out All-Star Mark Langston. Omar Vizquel also made his MLB debut for the Mariners, and fellow future All-Stars Edgar Martínez and Jay Buhner played limited roles for the team.

In August, owner George Argyros sold the team to Jeff Smulyan.

First-time MLB manager Jim Lefebvre was hired in November 1988, replacing interim manager Jim Snyder, who was fired in October. He would lead the team to their first winning record in the 1991 season, his final year at the helm.

Note: Pos = Position; G = Games played; AB = At bats; R = Runs scored; H = Hits; HR = Home runs; RBI = Runs batted in; Avg. = Batting average; SB = Stolen bases

Note: G = Games played; AB = At bats; H = Hits; Avg. = Batting average; HR = Home runs; RBI = Runs batted in

Note: G = Games pitched; IP = Innings pitched; W = Wins; L = Losses; ERA = Earned run average; SO = Strikeouts

Note: G = Games pitched; IP = Innings pitched; W = Wins; L = Losses; ERA = Earned run average; SO = Strikeouts