Kowar committed to play college baseball for Clemson University as a high school sophomore but was granted his release following a coaching change.[5] He instead chose to attend the University of Florida.[6] He was roommates with future Royals teammate Brady Singer.[2] As a freshman in 2016 for the Gators, Kowar appeared in 12 games, pitching to a 3–0 record and 3.37 ERA with 44 strikeouts in 34+2⁄3 innings pitched. His season ended in May due to a collapsed lung.[7][8][5] He returned in 2017 and went 12–1, tying Florida's best single-season record in school history, along with posting a 4.08 ERA with 84 strikeouts in 19 games.[9] During the 2017 College World Series, Kowar earned the save in the championship game, pitching 1+2⁄3 scoreless innings in his only relief appearance on the season, clinching Florida's 2017 national title.[5][10] In 2018, as a junior, Kowar was named to the All-SEC second team.[11] He finished his junior year with a 10–5 record and a 3.04 ERA in 18 starts.[12]
Kowar did not play in a game in 2020 due to the cancellation of the minor league season because of the COVID-19 pandemic.[20] He was selected to the team's alternate site for training during the abbreviated MLB season.[21] Kowar began the 2021 season with the Omaha Storm Chasers of the Triple-AEast league.[22] In six games to begin the year, Kowar had a 5–0 record and 0.85 ERA with 41 strikeouts in 31+1⁄3 innings pitched.[23]
On June 6, 2021, the Royals announced Kowar would be promoted to the major leagues to be the starting pitcher the following day against the Los Angeles Angels.[24] He was officially selected to the active roster on June 7.[25] In his debut, Kowar gave up four earned runs, allowed three hits, walked two batters, and threw three wild pitches before he was removed from the game in the first inning, getting only two outs.[26] In 9 appearances (8 starts) during his rookie campaign, Kowar posted a ghastly 0–6 record and 11.27 ERA with 29 strikeouts in 30+1⁄3 innings pitched. He received the Paul Splittorff Pitcher of the Year award from the Royals, given to the franchise's best minor league pitcher.[27]
In 2022, Kowar struggled in both Omaha and Kansas City. Starting 20 games for the Storm Chasers, he worked to a 4–10 record and 6.16 ERA with 88 strikeouts in 83+1⁄3 innings pitched. He limped to a 9.77 ERA with 17 strikeouts in 15+2⁄3 innings of work across 7 relief appearances for the Royals.[28]
Kowar began the 2023 season in Omaha and was called up to the Royals four times, sticking with the team after being recalled on August 17.[29][30] In 23 appearances relief for Kansas City, Kowar struggled to a 6.43 ERA with 29 strikeouts across 28 innings of work.[30]
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