Aug 14, 2023; Kansas City, Missouri, USA; Seattle Mariners relief pitcher Isaiah Campbell (49) pitches during the seventh inning against the Kansas City Royals at Kauffman Stadium. Mandatory Credit: Jay Biggerstaff-Imagn Images Jay Biggerstaff-Imagn Images

Diamondbacks Sign Former Mariners Reliever

Originally posted on Arizona Diamondbacks on SI
By Alex D'Agostino | Last updated Dec 9, 2025 7:00 PM ET

According to the Arizona Diamondbacks' transaction log page, the D-backs have signed right-handed reliever Isaiah Campbell to a minor league contract.

Arizona needs a great deal of relief help this offseason, with an injury-riddled major league bullpen and dwindling minor league depth options.

Campbell is the third reliever to sign a minor league deal (with a Spring Training invite) with the D-backs in the past week, joining Taylor Rashi (who returns to the organization) and Gerardo Carrillo.

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Arizona Diamondbacks Sign Isaiah Campbell

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Campbell was selected 76th overall in the 2019 MLB Draft by the Seattle Mariners. He spent three years in their system before making his major league debut in 2023.

Campbell enjoyed a high level of success in his first regular MLB workload, delivering a 2.83 ERA and 3.32 FIP over 27 appearances (28.2 innings) for Seattle.

Following that 2023 campaign, Campbell was traded to the Boston Red Sox in exchange for infielder Jose Urias. Campbell made a handful of appearances for Boston's big league club, but never made much of a significant major league impact.

In 2024, he posted a 16.20 ERA, getting blown up for 12 earned runs in just 6.2 innings. He allowed six runs in 7.2 innings in 2025, and spent most of the past two seasons with the Red Sox's Triple-A club.

He was more effective at that level in 2024 and 2025, however. He posted a 2.20 ERA in a limited 14-game Triple-A sample in 2024, then followed it up with a workhorse 2025 in which he pitched to a 3.90 ERA — while also picking up nine saves.

Campbell's profile fits the new identity the D-backs appear to be seeking with their minor league pitching. He features a mid-to-high-90s four-seam and a hard 90 MPH slider he leaned on 42% of the time in 2025, with a more horizontally-moving sweeper and occasional curve.

Arizona has yet to make any significant major league additions to their bullpen this offseason. While they have reportedly agreed to a deal with starter-reliever hybrid Michael Soroka for a one-year contract, he's expected to be primarily used as a starter.

The D-backs have expressed interest in former Rays closer Pete Fairbanks, and it was recently reported that they have interest in former Braves reliever Pierce Johnson.

While Campbell doesn't figure to be a major league contributor right away, there is almost always need for bullpen depth at any level.