Offseason
- November 18, 1980: Brad Gulden was traded by the New York Yankees with $150,000 to the Seattle Mariners for a player to be named later and Larry Milbourne. The Seattle Mariners sent back Brad Gulden (May 18, 1981) to the New York Yankees to complete the trade. In effect, Brad Gulden was traded for himself.
- December 8, 1980: Gary Gray was selected by the Mariners from the Cleveland Indians in the rule 5 draft.
- December 12, 1980: Byron McLaughlin was traded by the Mariners to the Minnesota Twins for Willie Norwood.
- December 12, 1980: Willie Horton, Larry Cox, Rick Honeycutt, Mario Mendoza, and Leon Roberts were traded by the Mariners to the Texas Rangers for Richie Zisk, Rick Auerbach, Ken Clay, Jerry Don Gleaton, Brian Allard, and Steve Finch (minors).
- March 26, 1981: Dave Heaverlo was released by the Mariners.
- March 26, 1981: Willie Norwood was released by the Seattle Mariners.
Read more about this topic: 1981 Seattle Mariners Season