Malachi made his major league debut on August 17, 2020, working a game between the Oakland Athletics and the Arizona Diamondbacks at Chase Field. He was at second base, with Mike Muchlinski at first, Marvin Hudson at third, and Brian Knight at home plate.^[7] Moore worked 156 MLB games before being hired as a full time umpire in 2023, and assumed uniform number 44 in honor of his mentor Kerwin Danley, who wore it before retiring after the 2021 season.

On June 20, 2024, he umpired second base for the MLB at Rickwood Field game in Birmingham, Alabama. The game was a tribute to the Negro leagues and featured the first all-Black umpiring crew in MLB history.  His first postseason assignment was the 2024 American League Wild Card Series between the Kansas City Royals and the Baltimore Orioles.