1984 Seattle Mariners season

The Seattle Mariners season was their eighth since the franchise creation. They finished fifth in the American League West with a record of .450.

Offseason

 * November 21, 1983: Bill Caudill and Darrel Akerfelds were traded to the Oakland Athletics for Dave Beard and Bob Kearney.
 * December 5, 1983: Dave Geisel was selected by the Mariners from the Toronto Blue Jays in the rule 5 draft.
 * January 17, 1984: Mike Blowers was selected in the eighth round of the amateur draft, but did not sign.
 * March 23, 1984: Rick Sweet was released by the Mariners.

Regular season

 * September 1 – Manager Del Crandall (.430) was fired on Saturday morning, August 31, succeeded by third base coach Chuck Cottier.
 * First baseman Alvin Davis reached base in each of the first 47 games of his career, and was chosen for his only All-Star Game. The M's MVP, he was also voted the American League's Rookie of the Year, with a .284 batting average, 27 home runs, and 116 RBIs.
 * Lefthanded starting pitcher Mark Langston became the first rookie since Herb Score to lead the American League in strikeouts; he was second in the balloting to teammate Davis for AL Rookie of the Year

Regular season

 * - style="text-align:center;"
 * Legend:      = Win       = Loss       = Postponement Bold = Mariners team member

Starters by position
''Note: Pos = Position; G = Games played; AB = At bats; H = Hits; Avg. = Batting average; HR = Home runs; RBI = Runs batted in''

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

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

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

Relief pitchers
Note: G = Games pitched; W = Wins; L = Losses; SV = Saves; ERA = Earned run average; SO = Strikeouts

Awards and honors

 * Mark Langston – American League Leader, Strikeouts (204)

All-Star Game