[10] Following his junior season, Harris was selected by the Oakland Athletics in the third round of the 2018 Major League Baseball draft and signed.
[16][17] Over 15 games (13 starts) between the two clubs, Harris pitched to a 1–5 record with a 2.80 ERA, striking out 65 batters over 54+2⁄3 innings.
[20] He was selected to play in the Arizona Fall League for the Mesa Solar Sox after the season with whom he gave up eight earned runs and 14 walks, alongside striking out 14 batters, over ten innings.
[25] On November 15, 2022, the Athletics selected Harris's contract and added him to the 40-man roster to protect him from the Rule 5 draft.
[28] After initially appearing in three games as a reliever, Harris made his first career MLB start against Pittsburgh on June 7.