Marlins promote Justin King to Triple-A Jacksonville roster

Justin King’s move to Jacksonville put one of the Marlins’ more interesting left-handed arms into the organization’s final proving ground. Listed as an active pitcher on the Jumbo Shrimp roster, King brings a 2.70 ERA, 18 strikeouts and just 10.0 innings over seven appearances in 2026, production that suggests strikeout ability is already a calling card.

The 28-year-old, born Dec. 19, 1997, in Lloydminster, Alberta, Canada, stands 6-foot-1 and 215 pounds and throws left-handed. On paper, that combination gives Miami a useful bullpen profile: a mature arm, a compact build, and enough swing-and-miss to matter if the command holds. King’s 2026 line is promising, and his career minor league numbers, 6-8 with a 4.24 ERA in 112 games, show a pitcher who has spent enough time in the system to understand the difference between raw stuff and sustained Triple-A execution.

Jacksonville is exactly where the Marlins can find that answer. The Jumbo Shrimp opened their International League season on March 27 and entered 2026 as the reigning Triple-A national champions, a status that has turned the affiliate into more than a stopover. It is the pressure point where Miami can sort out whether an arm is ready to help in the majors now or still needs refinement in the strike zone, in leverage, or in how he handles back-to-back outings.

King’s placement also fits a larger roster pattern. Jacksonville’s pitching staff is crowded, with several active arms and multiple pitchers already on the MLB 40-man roster, which makes the club a critical hub for depth and workload management. That kind of traffic is part of the Marlins’ larger organizational priority: keep arms moving, keep them fresh, and keep the next option close enough to matter quickly.

The recent shuffle involving Austin Slater underlined that role. Miami outrighted Slater to Jacksonville on April 25, and he elected free agency the next day, another reminder that the Jumbo Shrimp serve as the bridge between the majors and the rest of the system. For King, the assignment is an immediate test of how much of his profile is already big-league ready. The strikeouts are there. The next step is proving that the fastball shape, command and consistency can survive the sharper margins of Jacksonville, where relevance can arrive just as fast as the promotion did.