Mears reached the Double-A Altoona Curve in his first full professional season, though he spent the bulk of the season with the High-A Bradenton Marauders. Across three levels in 2019, Mears threw 46.2 innings, striking out 69 while walking just 18, maintaining a 3.28 ERA while being used exclusively out of the bullpen.
Mears was called up to the majors for the first time on August 8, 2020[2] and made his major league debut that night, pitching one inning, allowing one run, against the Detroit Tigers. Mears made four appearances with the Pirates that season, throwing five innings and giving up three runs.
Mears began the 2021 season at the Alternate Training Site, and joined the Triple-A Indianapolis Indians when their season began in May. Recalled to the Pirates for the first time on May 26, he didn't make an appearance until his fourth stint with the major league team, which began on July 20.[3][4]
Mears was placed on the 60-day injured list to begin the year on March 15, 2022, after undergoing arthroscopic surgery on his right elbow.[5] He was activated on August 20, and optioned to Triple–A Indianapolis.[6] On December 18, 2022, Mears was designated for assignment following the acquisition of Connor Joe.
Colorado Rockies
On December 23, 2022, Mears was claimed off waivers by the Texas Rangers.[7] Four days later, Mears was designated for assignment to make room for free-agent signing Nathan Eovaldi.[8]
On January 6, 2023, Mears was claimed off waivers by the Colorado Rockies.[9] He was optioned to the Triple-A Albuquerque Isotopes to begin the 2023 season.[10] In 16 games for the Rockies, Mears posted a 3.72 ERA with 21 strikeouts.
Mears made 41 appearances out of the bullpen for Colorado in 2024, registering a 5.56 ERA with 57 strikeouts across 45+1⁄3 innings pitched.