Johnson attended Faith Christian Academy in Arvada, Colorado, where he played baseball for three seasons on the varsity team.

He finished his first year at Missouri State with a 6–5 win–loss record and a 4.76 earned run average (ERA) in 75+2⁄3 innings pitched.

Johnson stayed with the Smokies during the 2015 season, where he posted a 6–2 record with a 2.08 ERA, holding batters to a .223 batting average.

[13] On December 23, 2019, Johnson signed a two-year contract which includes a third-year club option with the San Diego Padres of Major League Baseball (MLB).

On June 9, 2023, the Rockies announced that Johnson would be removed from the closer role, with Justin Lawrence and Jake Bird named as candidates to fill the position.

[18] On July 23, 2023, Johnson was traded to the Atlanta Braves in exchange for minor league prospects Victor Vodnik and Tanner Gordon.