2026 Seattle Mariners season

The 2026 Seattle Mariners season will be the 50th season in franchise history and their 27th full season at T-Mobile Park, their home ballpark in Seattle, Washington. The Mariners will open and close their season in Seattle, with opening day season on March 26, 2026 against the Cleveland Guardians and the regular season finale on September 27 against the Los Angeles Angels. The team is looking to improve their performance from their previous season, where they reached the 2025 American League Championship Series.
The Mariners plan to retire Randy Johnson's uniform number 51 on May 2. The number was retired in the 2025 season for Ichiro Suzuki. The Mariners will wear a uniform patch commemorating their 50th season.

Offseason

Coming off an AL West division title and American League Championship Series appearance, the Mariners acted early in the offseason, re-signing first baseman Josh Naylor, who had been a 2025 mid-season pickup, to a five-year contract in mid-November 2025.
On December 5, the Mariners announced their coaching staff for the upcoming season. Two former coaches left for bench coach jobs, with third base coach Kristopher Negrón joining the Pittsburgh Pirates and bullpen coach Tony Arnerich going to the Cleveland Guardians. Carlos Cardoza, previously the Frisco RoughRiders manager, was named the third base coach, and former Mariner catcher Austin Nola began his coaching career as the bullpen coach. Jake McKinley, formerly the Nevada Wolf Pack coach, was named the field coordinator, replacing Louis Boyd, who took another role with the Mariners. Seattle retained all other coaches from 2025.

November 2, 2025: Josh Naylor, Eugenio Suárez, Caleb Ferguson and Luke Jackson elected free agency.
November 3: The Mariners declined Mitch Garver's $12 million mutual option, paying him a $1 million buyout and making him a free agent.
November 5: Pitcher Cole Wilcox traded by the Tampa Bay Rays to Seattle for cash.
November 6: Jorge Polanco declined a $6 million option, receiving a $750,000 buyout, and elected free agency. The Mariners claimed pitcher Ryan Loutos off waivers from the Washington Nationals.
November 16: Minor league pitcher Robinson Ortiz traded by the Los Angeles Dodgers to Seattle for minor league pitcher Tyler Gough.
November 17: Naylor signed a five-year, $92.5 million contract with the Mariners.
November 18: The Boston Red Sox traded minor league pitcher Alex Hoppe to the Mariners for minor league catcher Luke Heyman. The Mariners designated pitcher Tayler Saucedo for assignment. Saucedo elected free agency two days later.
November 21: The Mariners non-tendered Trent Thornton and Gregory Santos, making them free agents.

Source

Sources
The Mariners will have a new Single-A affiliate in 2026, as Diamond Baseball Holdings moved the Modesto Nuts after the 2025 season to San Bernardino to become the Inland Empire 66ers.