[7] Mayo did not play in a professional game after signing due to the cancellation of the minor league season because of the COVID-19 pandemic.
[9] He made his professional debut that July with the Rookie-level Florida Complex League Orioles and was promoted to the Delmarva Shorebirds of the Low-A East in August.
[9] Over 53 games between the two clubs, Mayo slashed .319/.426/.555 with nine home runs, 41 RBIs, 14 doubles, and 11 stolen bases.
[10] Following the season's end, he spent time at Ed Smith Stadium participating in Baltimore's fall instructional league.
[11] He was assigned to the Aberdeen IronBirds of the High-A South Atlantic League to begin the 2022 season.
[19] Mayo was a non-roster invitee to Orioles spring training in 2024 and batted .326 with one home run and 11 RBIs.
[23] His first MLB hit was a fifth-inning leadoff single to left field off DJ Herz to end a 0–for–16 slump in a 4–1 home win over the Washington Nationals twelve days later on August 14.