The Tampa Bay Rays selected Sullivan in the 17th round, with the 508th overall selection, of the 2015 Major League Baseball draft.[1] He played in 65 games for the rookie-level Princeton Rays in his first professional campaign. He spent the 2016 season with the Single-A Bowling Green Hot Rods, posting a .283/.314/.438 slash line with 13 home runs, 81 RBI, and 17 stolen bases in 118 games for the team.[3] In 2017, Sullivan split the year between the High-A Charlotte Stone Crabs and Double-A Montgomery Biscuits, hitting a cumulative .294/.324/.433 with 8 home runs, 74 RBI, and 18 stolen bases in 107 games.[4]
Sullivan played in 111 games for Montgomery in 2018, batting .266/.322/.380 with 7 home runs, 65 RBI, and 17 stolen bases. He returned to Montgomery for a third season in 2019. On June 6, 2019, Sullivan hit for the cycle in a game against the Tennessee Smokies.[5] He finished the year playing in 102 games, hitting .280/.333/.459 with 10 home runs, 51 RBI, and a career-high 21 stolen bases.[6]
Sullivan did not play in a minor league game in 2020 due to the cancellation of the minor league season because of the COVID-19 pandemic.[7] He spent the 2021 season with the Triple-A Durham Bulls, playing in 90 games and batting .223/.302/.375 with 9 home runs, 35 RBI, and 7 stolen bases. He elected free agency following the season on November 7, 2021.[8]
San Diego Padres
On December 1, 2021, Sullivan signed a major league deal with the Milwaukee Brewers.[9] On April 6, 2022, the Brewers traded Sullivan and Korry Howell to the San Diego Padres in exchange for Víctor Caratini.[10] He spent the season with the Triple-A El Paso Chihuahuas, hitting .285/.339/.444 with 9 home runs and 81 RBI (tying a career-high) in 113 games.[11] He was assigned to El Paso to begin the 2023 season.
On April 16, 2023, Sullivan was promoted to the major leagues for the first time after Luis Campusano suffered a left thumb sprain.[12] He made his MLB debut on April 18 as the starting catcher in a game against the Atlanta Braves.[13] In 33 games during his rookie campaign, Sullivan batted .210/.244/.284 with one home run and six RBI.
Sullivan was optioned to Triple–A El Paso to begin the 2024 season.[14] On April 16, Sullivan was called up for the first time in 2024.[15]