Mariners former reliever Trent Thornton reportedly signs with Cubs

Trent Thornton has found a new home in Chicago, while the Seattle Mariners arguably still need to find one more quality arm for the bullpen.

As the Mariners continue to look for more help in their bullpen, former mainstay Trent Thornton is now headed to Chicago. As per Zac Hereth of Seattle Sports, the righty has signed a major league deal with the Cubs for the 2026 season.

Thornton had a rough year in 2025 with the Mariners, first with an appendicitis which required surgery and then ending prematurely at the beginning of August after tearing his left Achilles. (He even suffered heatstroke and collapsed during a game, ironically against the Cubs.) After the season concluded he was non-tendered and subsequently became a free agent.

Even allowing for these issues, Thornton struggled overall for the M’s as evidenced by a -0.1 bWAR, 4.68 ERA, 4.74 FIP and 1.299 WHIP in 42.1 combined innings over 33 appearances. His Baseball Savant page further displayed the issues, highlighted by ranking in the 28th percentile for Extension and 50th percentile for Fastball Velo.

Trent Thornton had his moments in Seattle

It wasn’t always so challenging for Thornton in Seattle, particularly when he first arrived in a trade from the Toronto Blue Jays at the Aug. 1 deadline in 2023. He made an immediate positive impact with a 2.08 ERA, 1.077 WHIP and 0.3 fWAR in 26.0 innings over 23 appearances.

Thornton went on to become a vital part of the bullpen the following year in Seattle, as he appeared in a major league career-high 71 games. Over 72.1 combined innings for the Mariners he produced a 0.3 bWAR, 3.61 ERA and 1.134 WHIP.

In fairness to Thornton, pending his full recovery he has the potential to be a useful asset for the Cubs. While he did have issues last year in Seattle, it should be added that he recorded a 2.28 ERA, 2.42 FIP, 1.06 WHIP and 0.4 fWAR in 23.3 innings over his final 15 appearances prior to the season-ending injury.

Thornton will always be remembered fondly in the Pacific Northwest, with him providing a memorable highlight after the Mariners clinching a playoff spot last season, versus the Colorado Rockies. Despite his injury he celebrated with his teammates by riding his scooter around the bases, and we join others in wishing him all the best in Chicago.

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Mariners bullpen must be better in 2026

As for the Mariners, it will be interesting to see what lies ahead for a bullpen which didn’t have much quality depth last year behind Andrés Muñoz, Matt Brash, Gabe Speier and Eduard Bazardo. They did acquire Caleb Ferguson at the trade deadline, but he failed to live up to expectations.

The bullpen did rank ninth in 2025 with a team ERA of 3.72 and eighth in fewest walks, but they were also 13th in WHIP, tied-16th in opposing batting average and 17th in strikeouts. The lack of quality depth combined with ongoing injury issues ultimately proved costly for the M’s in the playoffs and it does need to be better this coming season.

Aside from the core of Muñoz, Brash, Speier and Bazardo, the Mariners have since added lefty Jose Ferrer from the Washington Nationals, although it did mean giving up top rated catching prospect Harry Ford. The M’s have also acquired Yosver Zulueta from the Cincinnati Reds, but arguably still need one more quality arm to compliment the bullpen.

Photos court​‌esy of Tim Rogers Photography

Where do you stand on the Mariners bullpen as a whole right now, pending any further moves. Do you expect them to be about the same as last season, better, or worse? Let us know your thoughts in the comments section below.