St. Louis Cardinals in 2017|leftIn July 2013, at age 17, Alcántara signed with the
St. Louis Cardinals as an international free agent. He made his professional debut in 2014 with the
Dominican Summer League Cardinals and spent the whole season there, going 1–9 with a 3.97
ERA in 12 games (11 starts). He spent 2015 with the
Gulf Coast Cardinals where he pitched to a 4–4 record and 3.22 ERA in 12 games started, and started 2016 with the
Peoria Chiefs. During a start in May he tied the Chiefs record with 14 strikeouts. He was promoted to the
Palm Beach Cardinals in July 2016. He finished the 2016 season with a combined 5–11 record with a 3.96 ERA in 23 games started between both clubs. Alcántara began 2017 with the
Springfield Cardinals. After pitching to a 7–5 record and 4.31 ERA while 4th in the league in walks and leading it with 20 wild pitches in a career high 125.1 innings, the Cardinals promoted him to the major leagues on September 1, 2017. After the season, the Cardinals assigned Alcántara to the
Surprise Saguaros of the
Arizona Fall League (AFL), where he was selected to the Fall Stars Game. He pitched 15 total innings in the AFL, finishing the season with five games started, a 1–2 record, and a 4.20 ERA.
Miami Marlins On December 14, 2017, the Cardinals traded Alcántara, along with
Magneuris Sierra,
Zac Gallen, and
Daniel Castano to the
Miami Marlins for
Marcell Ozuna.
MLB.com ranked Alcántara as Miami's third-best prospect going into the 2018 season. He began 2018 with the
New Orleans Baby Cakes, and was recalled by Miami on June 28. He made his Marlins debut on June 29 as the
starting pitcher, pitching five innings in which he gave up one run on three hits and five walks while striking out two, earning the win as Miami defeated the
New York Mets 8–2. He was placed on the 10-day
disabled list on with a right axillary infection. On May 19, 2019, Alcántara pitched his first career shutout, an 89-pitch two-hit
Maddux against the New York Mets. Alcántara was the sole Miami Marlins player named to the
2019 Major League Baseball All-Star Game. Pitching the eighth inning, he retired the side. He finished the season with a 6–14 record and a 3.88 ERA over innings in 32 starts, leading the National League in losses and shutouts. In the shortened 2020 season, Alcántara was 3–2 with a 3.00 ERA in 42 innings. Alcántara owns Marlins franchise records of most innings pitched by a rookie, and most innings pitched and strikeouts by a Dominican-born player. On November 28, 2021, the Marlins signed Alcántara to a contract extension worth $56 million, breaking the record for the largest contract for a pitcher under team control with less than four years service time set by
Carlos Martinez. In 2022, he was 14–9 with a 2.28 ERA in 32 starts covering 228.2 innings. With a
bWAR of 8.0, Alcántara led the
National League, and led all pitchers across both leagues. He unanimously won the 2022
NL Cy Young Award, over second-place pitcher
Max Fried. Alcántara regressed from his Cy Young campaign in 2023, making 28 starts and posting a 7–12 record and 4.14 ERA with 151 strikeouts in innings pitched. On September 4, 2023, he was placed on the injured list with a right forearm flexor strain. An
MRI later revealed a sprain of Alcantara's
ulnar collateral ligament, putting his season in jeopardy. He began a rehab assignment with the Triple–A
Jacksonville Jumbo Shrimp, but was shut down for the remainder of the season on September 23 after experiencing forearm tightness. On October 6, Alcántara underwent
Tommy John surgery to repair the
UCL in his right elbow, ruling him out for the 2024 season. Returning from injury in 2025, Alcántara had an up-and-down season. In the first half, Alcántara struggled mightily, slumping to a 2–7 record by the end of May. After three straight starts allowing 5 or more
earned runs in July, Alcántara sat at a 7.14 ERA, the highest of any starter in MLB up to that point in the season. However, from this point on, Alcántara settled down, and recorded numerous solid outings, including 3 straight 7-inning starts from August 20 against the
St. Louis Cardinals, to August 31, against the
New York Mets, logging two wins in this span. A 3–1 record in September lifted Alcántara to a final 11–12 record, and a 5.36 ERA. Following his final start of the season, an emotional Alcántara reflected upon his season and leadership role within the Marlins clubhouse, explaining after the game that he was "just trying to take every special moment that I had with my teammates". A subject of trade talks throughout the season, Alcántara ultimately remained with the team for the 2026 season. In 2026, Alcántara was selected for his franchise record sixth Opening Day start for the Marlins, where he pitched 7 shutout innings with 5 strikeouts against the
Colorado Rockies, earning the win. He followed this up with a complete–game shutout against the
Chicago White Sox on April 1, striking out seven, and allowing just three hits in a 10–0 romp. ==Pitching style==