Arizona Diamondbacks After signing, Weiss made his professional debut with the
Rookie-level Arizona League Diamondbacks before being promoted to the
Hillsboro Hops of the
Low–A Northwest League. Over innings, he compiled a 3.86 ERA. Weiss began the 2019 season with the
Single–A Midwest League Kane County Cougars and was later promoted to the
Visalia Rawhide of the
High–A California League, pitching innings to an 8–7 record and a 4.07 ERA over 26 starts between both teams. He did not play in a game in 2020 due to the cancellation of the minor league season because of the
COVID-19 pandemic. In 2021, Weiss began the year with the
Amarillo Sod Poodles of the
Double-A Central and was promoted to the
Reno Aces of the
Triple-A West in July. Over 34 appearances (eight starts) between the two clubs, Weiss went 6–3 with a 4.60 ERA and 88 strikeouts over innings. On November 19, 2021, the
Diamondbacks selected Weiss' contract and added him to their 40-man roster. He opened the 2022 season with Amarillo and was promoted to Reno in late May. On June 26, he was designated for assignment following the promotion of
Dallas Keuchel.
Kansas City Royals On July 1, 2022, Weiss was claimed off waivers by the
Kansas City Royals and optioned to the Triple-A
Omaha Storm Chasers. In 30 games out of the
bullpen for Omaha, Weiss registered a 2–2 record and 7.82 ERA with 34 strikeouts in innings pitched. Following the season, on October 26, he was removed from the
40-man roster and sent outright to Triple–A. Weiss was assigned to Triple–A Omaha to begin the 2023 season. In 12 appearances, he struggled to a 7.07 ERA with 15 strikeouts in 14.0 innings of work. Weiss was released by the Royals organization on May 20, 2023.
High Point Rockers On June 6, 2023, Weiss signed with the
High Point Rockers of the
Atlantic League of Professional Baseball. He made 9 starts for the Rockers, posting a 5–3 record and 4.61 ERA with 52 strikeouts in innings pitched. On July 29, Weiss was released by High Point.
Fubon Guardians On August 3, 2023, Weiss signed with the
Fubon Guardians of the
Chinese Professional Baseball League (CPBL). In 5 starts for the Guardians, he registered a 4–1 record and 2.32 ERA with 25 strikeouts across 31 innings. Weiss became a free agent following the season.
High Point Rockers (second stint) On April 15, 2024, Weiss signed with the
High Point Rockers of the
Atlantic League of Professional Baseball. In 9 starts for the Rockers, Weiss compiled a 3–4 record and 4.34 ERA with 73 strikeouts across innings of work.
Hanwha Eagles 2024 On June 16, 2024, Weiss' contract was purchased by the
Hanwha Eagles of the
KBO League. Weiss appeared in his first game for the Eagles on June 25, striking out seven
Doosan Bears batters in six scoreless innings of work. Alongside veteran major leaguers
Hyun-jin Ryu and
Jaime Barría in the starting rotation, Weiss contributed to the team posting a 14–10 record in August and making a surprise late entry into the race for the KBO playoffs. Weiss notably struck out 12
SSG Landers on August 16, and recorded a win against the champions–to–be
Kia Tigers in his final outing of the year on September 27. In 16 total starts for the '24 Eagles, he compiled a 5–5 record and 3.73 ERA with 98 strikeouts across innings pitched.
2025 On November 22, 2024, Weiss re–signed with Hanwha on a one–year, $950,000 contract. In 2025, the Eagles paired Weiss with international free agent
Cody Ponce as the team's front-line starters for the inaugural season at the new
Daejeon Hanwha Life Ballpark. Pitching in his first full season in Korea, Weiss appeared on the mound for a full slate of 30 starts, posting a 16–5 record and 2.87 ERA while striking out 207 batters across innings. He achieved his first 10-win season as a professional in a game against the
Kiwoom Heroes at the
Gocheok Sky Dome on July 7, where he struck out 11 batters and yielded only 2 hits in 6 innings, turning in the fifth of his eight total double-digit strikeout performances in 2025. The Eagles finished the regular season in second place, narrowly trailing only the
LG Twins. Behind career-high offensive performances by third baseman
Roh Si-hwan and left fielder Moon Hyun-bin, their strong rotation secured the team's first postseason berth since 2018. On October 24, the Ponce-Weiss duo defeated the
Samsung Lions in the deciding fifth game of the playoff round to earn the first trip to the
Korean Series for the Eagles since 2006. Appearing from the bullpen, Weiss was credited with the save as he completed the final 12 outs of the game after Ponce's quality start, sending the Eagles onward to Seoul. In the
2025 Korean Series, the Eagles were defeated 4–1 by the
LG Twins. Weiss started game 4 in Daejeon on October 30, facing a 1–2 deficit in the series. In a spirited outing where he threw 117 pitches across innings, he struck out seven and allowed only four hits, leaving the game in the top of the eighth inning with a 3–0 lead and Twins infielder Shin Min-jae on second base. Shin scored on a hit off of reliever Kim Seo-hyeon, plating the only run charged to Weiss in the Korean Series. The Twins went on to win game 4 in the ninth inning, erasing Weiss as the winning pitcher of record, and won the series in the conclusive fifth game.
Houston Astros On December 9, 2025, Weiss signed a one-year, $2.6 million contract with the
Houston Astros. Weiss competed for the starting pitcher role in the Astros' 2026 spring camp. He made his breakout spring performance in an exhibition game against the championship-winning Venezuelan World Baseball Classic team on March 3, where he struck out
Ronald Acuña Jr.,
Jackson Chourio, and
Eugenio Suárez, coincidentally appearing in the same inning as Venezuelan pitcher
Ricardo Sánchez who Weiss once replaced on the
KBO's
Hanwha Eagles. Weiss made his first appearance as a starting pitcher in major league spring training on March 14 and was named the winner against the
New York Mets and starter
Freddy Peralta. The
Houston Astros named Weiss to the opening day roster in 2026 as a relief pitcher, and he made his long-awaited major league debut on March 27 against the
Los Angeles Angels of Anaheim in
Houston,
Texas. He allowed a home run to his first batter faced in the major leagues,
Zach Neto, but Weiss recorded his first major league strikeout against
Jorge Soler. ==Personal life==