[3] Valdez had had verbal agreements with seven teams prior to signing with the Astros, but each offer was withdrawn after the results of his physical revealed that he might require ulnar collateral ligament reconstruction, also known as "Tommy John surgery."

[14] He led the club in innings pitched, tied for the team lead in games won,[15] and was named Astros Pitcher of the Year by the Houston chapter of the Baseball Writers' Association of America (BBWAA).

[17] Valdez went 3–1 in the postseason, which saw the Astros reach the American League Championship Series (ALCS) after winning the first two rounds of the COVID-affected 2020 season.

On March 3, 2021, Valdez suffered a fractured left ring finger after he was hit in the hand by a Francisco Lindor ground ball in a spring training game.

At several points during the game, Red Sox radio announcers Joe Castiglione and Will Flemming commented that Valdez was rubbing the fingers of his pitching hand against his cheek and temple each time he was given a new ball, which prompted an angry response from Houston sportswriters; no accusation of cheating was filed by the Red Sox.

[19] Valdez was the seventh visiting pitcher at Fenway to go at least eight innings in a postseason game while allowing a run or fewer, and the first since Charles Nagy in 1998.

[21] On April 7, 2022, Valdez won his debut as an Opening Day starting pitcher, recording 6+2⁄3 scoreless innings in a 3–1 game.

Twelve consecutive outs Valdez produced were via strikeout, supplanting the franchise record of nine previously accomplished by Don Wilson, Randy Johnson, and Gerrit Cole (twice).

[25] He pitched in the third inning of the All-Star Game, retiring all three batters faced, and received the win when the American League scored the go-ahead run after he had finished.

[27] Through September 14, 2022, Valdez had induced the highest career ground ball rate (66.3%) of any pitcher since 1988; only Derek Lowe had surpassed that figure in any individual season (2002 and 2006).

[28] Valdez threw 25 straight quality starts from April 25 to September 18, establishing the MLB record over a single season.

He led the AL in innings pitched (201+1⁄3), batters faced (827), complete games (3), shutouts (1), quality starts (26), and HR/9 IP (0.492), all of which were career-bests to that point.

His win total placed second in the AL behind teammate Justin Verlander, while his ERA was sixth, and 194 strikeouts were seventh,[14][35] tied with Cristian Javier for the team lead.

[38] Valdez started and became the winning pitcher in the Astros' Game 6 Series clincher, working six innings while allowing one run on two hits and striking out nine to give him his first career championship.

A $3.8 million raise, it was the largest to date for pitcher advancing from year 1 to 2 of arbitration who had yet to win a Cy Young Award.

[40] Valdez drew his second consecutive Opening Day start for the Astros, tossing a scoreless outing versus the Chicago White Sox.

[44] On August 25, Valdez departed after seven hitless innings, five walks surrendered and six strikeouts versus the Detroit Tigers; the no-hitter at Comerica Park remained intact until Kerry Carpenter singled off Bryan Abreu with one out in the eighth.

[51] In 3 playoff starts in 2023, Valdez surrendered 19 hits, 9.00 ERA, 1.037 on-base plus slugging (OPS) over 12 innings, struck out 17 and lost all 3 outings.

[64] Valdez is naturally right-handed and performs everyday tasks with his right hand; he taught himself to throw left-handed as a child knowing the value of such pitchers in baseball.

[65] During Game 2 of the 2022 World Series at Minute Maid Park, Valdez' father, José Antonio Valdéz Ramírez, witnessed his son pitch for the first time in the major leagues.