Méndez signed with the Texas Rangers as an international free agent in July 2011 out of Venezuela for $1.5MM. Mendez made his professional debut in 2012 with the DSL Rangers, posting a 2–1 record with a 1.99 ERA in 45.1 innings. In 2013 he made his stateside debut with the Spokane Indians, posting a 1–2 record with a 3.78 ERA in 33.1 innings. Mendez split the 2014 season between he AZL Rangers and Hickory Crawdads, posting a combined 3–1 record with a 2.70 ERA in 36.2 innings. Mendez spent the entire 2015 season with the Hickory Crawdads, posting a 3–3 with a 2.44 ERA in 66.1 innings. The Rangers added him to their 40-man roster after the 2015 season. Mendez split the 2016 minor league season between the High Desert Mavericks, Frisco RoughRiders, and the Round Rock Express. He posted a combined 12–3 record with a 2.19 ERA in 111 innings. After the trade deadline of the 2016 season, Mendez became the team's no. 2 prospect after the Rangers dealt Luis Ortiz and Lewis Brinson to the Brewers for catcher Jonathan Lucroy. Méndez was promoted to the Major Leagues during September call-ups on September 2, 2016 after having an ERA of 2.19 as a starter in the minors. He made his Major League debut on September 5coming out of the bullpen allowing five earned runs while pitching one inning against the Seattle Mariners. He appeared in just two games that September, throwing 3 innings with a 18.00 ERA. Mendez split the 2017 season between the Frisco RoughRiders and the Rangers. In 24 games with Frisco he posted a 7–8 with a 3.79 ERA in 137.2 innings. In 7 relief outings for the Rangers, he posted a 0–1 record with a 5.11 ERA in 12.1 innings. Mendez opened the 2018 season with the Round Rock Express. He was on the Rangers active roster when on June 19, he was optioned back to AAA for violating an unspecified team rule after a game in Kansas Citythe night prior. Mendez was demoted down to the Down East Wood Ducks on June 25, for what the organization called a "reset" on his development. Mendez worked his way back up through AA and AAA, before being recalled to the major league roster on September 2. Mendez posted a combined 2–10 record with a 4.71 ERA in 122.1 innings between the Down EastWood Ducks, Frisco Roughriders, and the Round Rock Express. In 8 games with the Rangers in 2018, Mendez posted a 2–2 record with a 5.53 ERA in 27.2 innings. During the 2018 offseason the Rangers announced that they were given a 4th minor league option on Mendez that would allow them to option him to the minor leagues during the 2019 season. On March 19, 2019, the team announced that Mendez would not need season ending surgery, instead he would be available by midseason. Mendez was placed on the 60-day injured list to open the 2019 season. He returned to Texas on September 5, and finished the season going 1–0 with a 5.79 ERA over innings.
