Seattle Mariners The
Seattle Mariners selected Williamson in the second round of the
2019 Major League Baseball draft and he signed. Williamson made his professional debut with the
Everett AquaSox, posting a 2.35 ERA over innings. Due to the cancellation of the 2020
Minor League Baseball season caused by the
COVID-19 pandemic, he did not pitch for a team, but was a member of the Mariners' 60-man player pool. Williamson returned to Everett to start 2021 and was promoted to the
Arkansas Travelers during the season. Over 19 starts between the two teams, he went 4–6 with a 3.39 ERA and 153 strikeouts over innings.
Cincinnati Reds On March 14, 2022, the Mariners traded Williamson,
Justin Dunn,
Jake Fraley, and a
player to be named later (
Connor Phillips) to the
Cincinnati Reds in exchange for
Jesse Winker and
Eugenio Suárez. Williamson began the 2022 season with the Double-A
Chattanooga Lookouts before receiving a promotion to the Triple-A
Louisville Bats later in the season. In 27 starts between the two, he worked to a 6–7 record and 4.11 ERA with 123 strikeouts in innings pitched. On November 15, the Reds added Williamson to their
40-man roster to protect him from the
Rule 5 draft. After making a push for a spot in the Reds’ rotation during spring training, Williamson was optioned to Triple-A Louisville to begin the 2023 season. In 8 starts, he struggled to a 2–4 record and 6.62 ERA with 27 strikeouts. On May 15, 2023, the Reds announced that Williamson would make his debut the next day as the starting pitcher against the
Colorado Rockies. In 23 starts during his rookie campaign, he logged a 5–5 record and 4.46 ERA with 98 strikeouts across 117 innings pitched. Williamson began the 2024 season on the injured list with a left shoulder strain. On May 8, 2024, he was transferred to the 60–day injured list. Williamson was activated on September 1. In 4 games (3 starts) for Cincinnati, he posted a 3.77 ERA with 12 strikeouts over innings pitched. On September 18, it was announced that Williamson had suffered a full tear of his
ulnar collateral ligament and would undergo
Tommy John surgery. The procedure ruled him out for the remainder of 2024, as well as the entirety of the 2025 season. On April 30, 2026, Williamson was placed on the injured list due to left shoulder fatigue. On May 6, he was transferred to the 60-day injured list. ==References==