SEA Mariners

The Mariners were created as a result of a lawsuit. In 1970, after Bud Selig bought the Seattle Pilots and moved them to Milwaukee to become the Milwaukee Brewers, the city of Seattle, King County, and the state of Washington (represented by then-state Attorney General and future U.S. Senator Slade Gorton) sued the American League for breach of contract. Confident that Major League Baseball would return to Seattle within a few years, King County built the multi-purpose Kingdome, which would become home to the National Football League's expansion Seattle Seahawks in 1976. The name "Mariners" was chosen by club officials in August 1976 from more than 600 names submitted by 15,000 entrants in a "name the team" contest. The name was submitted by Roger Szmodis of Bellevue, Washington. When the Mariners attempted to reach Szmodis about the prize he had won, they were unsuccessful—initially and ultimately.

The first home run in team history was hit on April 10, 1977, by designated hitter Juan Bernhardt.

That year, pitcher Diego Seguí, in his last major league season, became the only player to play for both the Pilots and the Mariners. The Mariners finished with a 64–98 record, matching the 1969 Pilots' record. The team avoided finishing in last place in the AL West by half a game. The Mariners would not post a winning record or finish above 4th place in any of their first 14 seasons. In 1979, Seattle hosted the 50th Major League Baseball All-Star Game. After the 1981 season, the Mariners were sold to California businessman George Argyros, who in turn sold the team in 1989 to a group led by Indianapolis-based Jeff Smulyan, who owned radio and television stations, for $76 million. Smulyan proposed moving the team to Tampa, Florida or another market in 1992 before he put the team up for sale. Nintendo of America bought the team in 1992; Nintendo CEO Hiroshi Yamauchi, who held a 49 percent share of the franchise, had never been to a baseball game but sought to thank the city for its role in the company's success.

Before the 1993 season, the Mariners hired manager Lou Piniella, who had led the Cincinnati Reds to victory in the 1990 World Series. Mariners fans embraced Piniella, and he would helm the team from 1993 through 2002, winning two American League Manager of the Year Awards during his tenure. (Piniella was selected by the Pilots in the 1968 expansion draft but did not play for Seattle, being traded in April 1969 to the Kansas City Royals, where he earned AL Rookie of the Year honors that year.)

The Mariners first won the AL West and made the playoffs in 1995, despite star outfielder Ken Griffey Jr. missing much of the season after breaking his wrist crashing into the center field wall. The team defeated the California Angels in a one-game playoff to win the division. The Mariners returned to the playoffs in 1997 and 2000.

The 2001 Mariners finished with a record of 116–46, leading all of Major League Baseball in winning percentage for the duration of the season and easily winning the American League West division title. In doing so, the team broke the 1998 New York Yankees' American League single-season record of 114 wins and matched the all-time MLB single-season record for wins set by the 1906 Chicago Cubs. At the end of the season, Ichiro Suzuki won the AL MVP, AL Rookie of the Year, and one of three outfield Gold Glove Awards, becoming the first player since the Fred Lynn in 1975 to win all three in the same season. The Mariners advanced through the postseason but lost to the Yankees in the 2001 ALCS. It would be the team's last playoff appearance until 2022.

The Mariners had a 93-win season in 2002 but failed to make the postseason. Manager Lou Piniella was traded to the Tampa Bay Rays during the offseason. The team repeated with 93 wins in 2003 and also did not qualify for the playoffs. On October 22, 2008 the Mariners announced the hiring of Jack Zduriencik, formerly scouting director of the Milwaukee Brewers, as their general manager. Weeks later, on November 18, the team named Oakland Athletics bench coach Don Wakamatsu as its new manager. The off-season also saw a litany of roster moves, headlined by a 12-player, 3-team trade that sent All-Star closer J. J. Putz to the New York Mets and brought 5 players, including prospect Mike Carp and outfielder Endy Chávez from New York and outfielder Franklin Gutiérrez from the Cleveland Indians, to Seattle. Many of the moves, like the free-agent signing of Mike Sweeney, were made in part with the hope of squelching the clubhouse infighting that plagued the Mariners in 2008. It also saw the return of Seattle favorite Griffey Jr. The 2009–10 offseason was highlighted by the trade for 2008 AL Cy Young Award winner Cliff Lee from the Philadelphia Phillies, the signing of third baseman Chone Figgins, and the contract extension of star pitcher Félix Hernández.

Griffey Jr. announced his retirement on June 2, 2010, after 22 MLB seasons. After its busy offseason and high expectations, the team flopped in 2010, finishing with the worst record in the American League. The Mariners fired Wakamatsu along with several coaches on August 9, 2010. Daren Brown, the manager of the Triple-A affiliate Tacoma Rainiers, took over as interim manager. Dave Niehaus, the Mariners' play-by-play announcer since the team's inception, died of a heart attack on November 10, 2010, at the age of 75. In memory of Niehaus, Seattle rapper Macklemore wrote a tribute song called "My Oh My" in December 2010. He performed the song at the Mariners' Opening Day game on April 8, 2011. The Mariners hired former Cleveland manager Eric Wedge as their new manager on October 19, 2010.

On April 21, 2012, Philip Humber of the Chicago White Sox threw the third perfect game in White Sox history against the Mariners in Seattle. It was the 21st perfect game in MLB history. Mariners starter Kevin Millwood and five relievers combined to throw the tenth combined no-hitter in MLB history, the first in Mariners history, on June 8. The six pitchers used in a no-hitter tied a major league record, first set by the Houston Astros in 2003. Félix Hernández pitched the first perfect game in team history, shutting down the Tampa Bay Rays 1–0 at Safeco Field on August 15. It was the 23rd perfect game in Major League Baseball history. The Mariners became the first team in Major League Baseball to be involved in two perfect games in one season.

Zduriencik was fired on August 28, 2015. Jerry Dipoto, a former general manager of the Los Angeles Angels of Anaheim, was hired as the Mariners' new general manager one month later. On October 9, manager Lloyd McClendon was fired. Scott Servais was named the new Mariners' manager on October 23.

Nintendo announced on April 27, 2016, that it would sell its controlling stake in the Mariners to First Avenue Entertainment limited partnership, led by John W. Stanton. Nintendo retained a 10 percent ownership share of the team after the sale was completed in August 2016. The franchise was valued at $1.4 billion at the time and included Root Sports Northwest, the team's regional television network.

The Stanton/Dipoto/Servais era was characterized by two competitive phases. In the first phase, the organization tried to contend for a championship with the existing core of Robinson Cano, Félix Hernández, Nelson Cruz, and Kyle Seager. The team came close but ultimately missed the playoffs. Following the 2018 season, the organization pivoted to a rebuild, trading several players for prospects. Following a fallow period of 2019–20, the team returned to contention in 2021, winning 90 games but falling short of the playoffs. In 2022, with a new core including Julio Rodríguez, J. P. Crawford, Cal Raleigh, Luis Castillo, George Kirby, and Logan Gilbert, the team reached the postseason for the first time since 2001. This broke what was at the time the longest playoff drought of any team in the "Big Four" North American sports. Rodríguez also won the American League Rookie of the Year Award. In 2023, the team won 88 games but finished one game out of a playoff spot. In August 2024, Servais was fired after blowing a 10 game lead over the second place team in the AL West, the Houston Astros, and having the team fall back to .500. Servais was replaced by the team's former catcher Dan Wilson as manager. The team again missed the playoffs by one game.