Justice was drafted by the Colorado Rockies in the fifth round, with the 140th overall selection, of the 2021 Major League Baseball draft.[4] He made his professional debut with the rookie–level Arizona Complex League Rockies. In 3 games, he logged a 3.00 ERA with 4 strikeouts in 3.0 innings of work.[5] Justice missed the entirety of the 2022 season due to a shoulder strain injury.[6]
Justice split the 2023 season between the High–A Spokane Indians, Double–A Hartford Yard Goats, and Triple–A Albuquerque Isotopes. In 38 combined games between the three affiliates, he posted a 3.49 ERA with 63 strikeouts, holding opposing batters to a .131 average.[7] On August 25, 2023, Justice was selected to the 40-man roster and promoted to the major leagues for the first time.[8] In 9 games during his rookie campaign, he struggled to an 8.59 ERA with 7 strikeouts across 7+1⁄3 innings pitched.
Justice was optioned to Triple–A Albuquerque to begin the 2024 season.[9]