In 2023, the Nationals named Alvarez their Minor League Pitcher of the Year; in 26 appearances (22 starts) for the Double-A Harrisburg Senators and Wilmington, he posted a combined 7–7 record and 2.99 ERA with 116 strikeouts across 129+1⁄3 innings pitched.[4] The Nationals named him their Minor League Pitcher of the Year.[5] Alvarez made 26 starts split between Harrisburg and the Triple-A Rochester Red Wings in 2024, pitching to a cumulative 8–9 record and 3.90 ERA with 114 strikeouts across 131+2⁄3 innings pitched.[6]
The Nationals promoted Alvarez to the major leagues on September 1, 2025.[7] He made his MLB debut that afternoon, starting against the Miami Marlins at Nationals Park.[8] He pitched five innings in a 2–0 Nationals victory, allowing one hit, striking out four, and walking two, becoming only the second Nationals starter in 15 years to win his major-league debut.[8] His catcher, C. J. Stubbs, also made his major-league debut that day, making Alvarez and Stubbs the first batterymates to make their MLB debuts together since 2023, and the first Nationals pitcher and catcher to do so since 2008.[8]
Alvarez was optioned to Triple-A Rochester to begin the 2026 season.[9]
