Martinez was drafted by the Texas Rangers in the 18th round of the 2011 Major League Baseball draft, out of Fordham University.[5] He made his professional debut with the AZL Rangers, and also appeared for the Low-A Spokane Indians, posting a cumulative 2.75 ERA across 10 contests. The next year, Martinez played for the Single-A Hickory Crawdads, pitching to a 8–6 record and 4.83 ERA across 31 appearances. Martinez split the 2013 season between the High-A Myrtle Beach Pelicans and the Double-A Frisco RoughRiders, logging a 12–7 record and 2.50 ERA with 128 strikeouts in 1511⁄3 innings of work.[6]
Martinez was named the Rangers' fifth starter on March 26, 2014.[7] He was formally selected to the 40-man roster on April 5 and promoted to the major leagues for the first time. In his first career start against the Tampa Bay Rays, Martinez went six innings, struck out three and allowed three earned runs on four hits. He received a no decision as the Rangers lost 5–4. After two straight starts against the Oakland Athletics, the Rangers got Matt Harrison back from the DL and moved Martinez to the bullpen. Martinez went 62⁄3 innings, struck out six and allowed only one earned run in four relief appearances. In a game against the Houston Astros, Harrison injured his lower back and had spinal fusion surgery. The Rangers then put Martinez back into the starting rotation.[8] Martinez finished his rookie season with a 5–12 record and 4.55 ERA in 29 major league contests. In 2015, Martinez posted an ERA of 3.96 and shared the major league lead in hit batsmen, with 13.[9] In 2016, Martinez split the year between the Triple-A Round Rock Express and Texas, recording a 2–3 record and 5.59 ERA in 12 big league games. In 2017, Martinez pitched to a 3–8 record and 5.66 ERA with 67 strikeouts in 1111⁄3 innings of work for Texas.
Hokkaido Nippon-Ham Fighters
Martinez with the Fighters in 2018
Upon reaching free agency and limited interest from MLB teams, Martinez signed a one-year, $1.8 million contract with the Hokkaido Nippon-Ham Fighters of Nippon Professional Baseball (NPB) on January 6, 2018. According to reports, the contract included possible incentives based on innings pitched.[10]
In his first NPB season, Martinez went 10–11 with 93 strikeouts and an ERA of 3.51. On December 18, 2018, Martinez re-signed with the team on a one-year, $2.2 million contract.[11] In 2019, Martinez pitched four innings. On October 18, 2019, Martinez signed a 1-year extension to remain with the Fighters.[12] In 2020, Martinez made 17 appearances for the Fighters, logging a 2–7 record and 4.62 ERA. On December 2, 2020, he became a free agent.[13]
On March 19, 2022, Martinez signed a major league contract with the San Diego Padres.[14] On November 10, Martinez opted out of his contract. On November 22, 2022, Martinez signed a three-year, $26 million contract with the Padres.[15]
Cincinnati Reds
On December 1, 2023, Martinez signed a two-year, $26 million contract with the Cincinnati Reds.[16] He declined his 2025 option on November 1, 2024 and became a free agent.[17]
However, on November 4, the Reds offered Martinez a qualifying offer, in which he accepted it on November 17, to remain with the team on a one-year contract.[18]
