For his 2016 performance at Mercer, Lewis was named an All-American, Baseball America's 2016 College Player of the Year, and won the 2016 Golden Spikes Award. He was selected in the first round of the 2016 Major League Baseball draft by the Seattle Mariners.
The Seattle Mariners selected Lewis with the 11th overall pick in the 2016 Major League Baseball draft.[14] He made his professional debut with the Everett AquaSox.[15] Lewis only played 30 games for the Everett AquaSox due to a right ACL injury,[16] batting .299 with three home runs and 26 RBIs. He spent 2017 with both the AZL Mariners and the Modesto Nuts, posting a combined .257 average with seven home runs and 31 RBIs in 49 games between both clubs, and 2018 with Modesto and the Arkansas Travelers, batting .244 with nine home runs and 52 RBIs in 86 games with the two teams.[17]
Lewis returned to Arkansas for the 2019 season,[18] hitting .263/.343/.398/.741 with 11 home runs and 62 RBI over 122 games.[19]
Seattle Mariners
The Mariners selected Lewis' contract and promoted him to the major leagues on September 10, 2019.[20] Lewis hit a home run off Trevor Bauer in his major league debut that night versus the Cincinnati Reds.[21][22] He hit home runs in each of his next two games as well, becoming the second player in history, after Trevor Story, to homer in each of his first three major league games.[23] He finished the 2019 season with a .268/.293/.592 slash line along with 6 home runs and 13 RBIs in 71 at bats.
In 2020, Lewis became the first Mariners player to be selected for the American League Rookie of the Year award since 2001, finishing the abbreviated season with a .262/.364/.437 slash line, 11 home runs, and 28 RBIs across 206 at bats.[24] He was awarded the title of American League Rookie of the Year by numerous other publications, including Sporting News.[25]
On June 1, 2021, Lewis was placed on the injured list after suffering a right meniscus tear.[26] He was placed on the 60-day injured list on June 18 and subsequently missed the rest of the season.[27]
Lewis went into MLB's concussion protocol after having been hit by a pitch on May 29, 2022. He returned to the active roster on July 22.[28] After continuing to struggle at the plate, and still dealing with issues related to his knee, Lewis was demoted to the Triple-A Tacoma Rainiers,[29] where he ended the 2022 season.
On January 13, 2023, Lewis agreed to a one-year, $1.61 million contract with the Diamondbacks, avoiding salary arbitration.[31] He was non-tendered and became a free agent on November 17.