Martínez signed with the Arizona Diamondbacks as an international free agent on March 5, 2018. He made his professional debut with the Dominican Summer League Diamondbacks. Martínez split the 2019 season between the DSL Diamondbacks, rookie–level Arizona League Diamondbacks, and rookie–level Missoula Osprey. In 18 games (10 starts) between the three affiliates, he recorded a 2.89 ERA with 78 strikeouts across 56.0 innings of work.[1] Martínez did not play in a game in 2020 due to the cancellation of the minor league season because of the COVID-19 pandemic.[2]
Martínez was optioned to the Triple-A Reno Aces to begin the 2023 season.[7] In 25 games for the Triple–A Reno Aces, he posted a 4.18 ERA with 38 strikeouts and 5 saves in 28.0 innings of work. On June 27, 2023, Martínez was promoted to the major leagues for the first time.[8] He went unused out of the bullpen and was optioned back to Reno on June 29, becoming a phantom ballplayer.[9] He was promoted for a second time on July 7, making his MLB debut the same day, allowing two runs in one inning against the Pittsburgh Pirates.[10][11] In 10 games during his rookie campaign, Martínez struggled to a 12.60 ERA with 14 strikeouts across 10.0 innings pitched.
Martínez was again optioned to Triple–A Reno to begin the 2024 season.[12]