In 2012, Valdez joined the Vaqueros Laguna of the Mexican League. He made 24 appearances and pitched to an 11–8 record, 5.27 ERA, and 84 strikeouts in 135 total innings. In the offseason, he returned to the Águilas del Zulia and later made five relief appearances for the Tigres del Licey of the Dominican Winter League. In 2013, Valdez returned to the Vaqueros Laguna, making 12 starts before being released on May 30.
On June 22, 2013, he signed with the Rieleros de Aguascalientes, and was released on June 27 after making one start for the team. After another offseason playing in the Venezuelan and Dominican Winter Leagues, Valdez did not play regular season baseball in 2014. He made seven appearances for the Bravos de Margarita during the 2014 offseason.
In 2015, he signed with the Olmecas de Tabasco. In 23 starts, Valdez went 13–8 with a 2.63 ERA and 161 strikeouts in 160 innings pitched. Valdez made five starts for the Tigres de Licey in the offseason.
On January 1, 2016, he signed a minor league contract with the Houston Astros and was invited to spring training. He spent the entire 2016 season with the Triple-A Fresno Grizzlies, and posted a 12–1 record, 3.12 ERA, and 114 strikeouts in 138 innings.
Oakland Athletics
In November 2016, he signed a minor league contract with the Oakland Athletics. He began the 2017 season with the Triple-A Nashville Sounds, but was recalled on April 21. After appearing in four games for Oakland with a 9.64 ERA, Valdez was designated for assignment on May 3.
Toronto Blue Jays
On May 5, 2017, Valdez was claimed off waivers by the Toronto Blue Jays and optioned to the Triple-A Buffalo Bisons. He was recalled on May 20. In July, Valdez was recalled by the Blue Jays and added to the starting rotation after Aaron Sanchez was placed on the disabled list. On July 25, Valdez earned his first MLBwin in over seven years, defeating the Oakland Athletics 4–1. In 2017 he threw a changeup 49.4% of the time, tops in MLB. Valdez was outrighted to Triple-A Buffalo on November 1, 2017, and elected free agency the following day.
Return to Tabasco
On March 16, 2018, Valdez signed with the Olmecas de Tabasco of the Mexican League. He was released on May 1, 2018.
On July 29, 2018, Valdez signed with the Leones de Yucatán of the Mexican League. In 2019, he pitched to a 15–2 record with a 2.26 ERA and 122 strikeouts across 147.2 innings, winning the league's pitcher of the year award. On January 4, 2020, Valdez requested and was granted his release in order to pursue an opportunity with an MLB-affiliated organization.
Baltimore Orioles
On January 10, 2020, Valdez signed a minor-league deal with the Baltimore Orioles.