In 2019, Cowser's freshman season at Sam Houston State, he was immediately placed into the starting lineup, and batted .361 with seven home runs, 54 runs batted in (RBI), and nine stolen bases over 56 games.[4] He won the Southland Conference Hitter of the Year Award.[5] He was also named a Freshman All-American by multiple media outlets including Baseball America, Collegiate Baseball Newspaper, Perfect Game, and D1Baseball.com.[6] Following the season, he earned a spot on the Team USA Collegiate National Team.[7] He was named Most Valuable Player of the 2019 USA vs Cuba Friendship Series after batting .438 with six runs.[8] Prior to the 2020 season, Cowser was named to the Golden Spikes Award watch list alongside earning pre-season Southland Conference honors.[9][10] Over 14 games for the 2020 season before the remainder of games were cancelled due to the COVID-19 pandemic, Cowser hit .255 with one home run.[4] As a junior in 2021, he slashed .374/.490/.680 with 16 home runs and 52 RBI over 55 games.[11] He was named the Southland Conference Player of the Year as well as being named to the All-Defensive Team.[12]
To open the 2023 season, Cowser returned to Norfolk.[23] In 56 games for the Tides, he hit .330/.459/.537 with 10 home runs and 40 RBI. On July 5, 2023, Cowser was selected to the 40-man roster and promoted to the major leagues for the first time.[24][25] He made his MLB debut that day in a 6–3 victory over the New York Yankees. In the 6th inning of the contest, Cowser recorded his first major league hit, an RBI single off reliever Nick Ramirez.[26] He spent the remainder of the campaign with the Tides after being optioned for a second time on September 3 when Aaron Hicks was reinstated from the injured list.[27] Cowser received the Most Valuable Player (MVP) Award at the Triple-A National Championship Game won by the Tides over the Oklahoma City Dodgers 7–6 on September 30. He went 2-for-4 with a two-out grand slam to center in the 7th inning.[28] With the Orioles, he batted .115/.286/.148 with no home runs and four RBI in 61 at–bats over 26 games.[29]
On March 24, 2024, it was announced Cowser had made the Orioles' Opening Day roster.[30] He drove in four runs in the first multi-RBI game of his MLB career in a 7–1 win over the Boston Red Sox on April 9.[31] He had another four-RBI performance when he hit the first two home runs of his MLB career in a ten-inning 9–4 victory over the same opponent two nights later on April 11. He had a total of ten RBI during the three-game sweep of the Red Sox at Fenway Park.[32] In 153 games for the Orioles, Cowser slashed .242/.321/.447 with 24 home runs and 69 RBI. For his performance, Cowser places 2nd in American League Rookie of the Year voting, losing to New York Yankees starting pitcher Luis Gil by 5 points, the second closest vote in awards history.
On October 2, 2024, Cowser was forced to exit Game 2 of the Wild Card Series against the Kansas City Royals an inning after taking a pitch off the hand while swinging. After the game, the Orioles announced that he suffered a broken left hand.[33] Cowser underwent successful surgery to repair the fracture on October 15.[34] He served as the master of ceremonies of the 2025 Major League Baseball draft lottery at the Winter Meetings on December 10, 2024.[35]
