The
Atlanta Braves selected Schwellenbach in the second round, with the 59th overall pick, of the
2021 Major League Baseball draft. He signed with Atlanta on July 19, 2021, for a $1 million
signing bonus. Shortly after signing, Schwellenbach underwent
Tommy John surgery to repair the
ulnar collateral ligament in his pitching elbow. He missed the entire 2022 season while rehabbing from surgery. Schwellenbach was assigned to the Single-A
Augusta GreenJackets at the start of the 2023 season. He was selected to play in the 2023
All-Star Futures Game. Schwellenbach split the beginning of the 2024 season with the High–A
Rome Emperors and Double–A
Mississippi Braves, accumulating a 1.80 ERA with 51 strikeouts across 8 starts. On May 29, 2024, Schwellenbach was selected to the
40-man roster and promoted to the major leagues for the first time. He made his MLB debut later that day against the
Washington Nationals, yielding three earned runs on five hits in five innings and earning the loss. He finished the 2024 season with a 4–1 record, 2.42 ERA, pitched 48 innings, and struck out 47 batters in 7 starts in his rookie year. On June 11, 2025, Schwellenbach pitched a complete game in a 6–2 win over the
Milwaukee Brewers, allowing five hits and two runs while striking out 9 batters on 104 pitches. It was the first complete game of his career. On June 28, Schwellenbach reached a career-high in a single game with 12 strikeouts against the
Philadelphia Phillies, where he pitched seven innings and allowing three hits and one earned run in a 6–1 victory. On July 2, he was placed on the 15-day injured list with a fractured elbow, and not expected to pitch until September. The Braves transferred Schwellenbach to the 60-day IL on July 6. On February 10, 2026, Schwellenbach was placed on the 60-day injured list due to inflammation in his right elbow. On February 18, Schwellenbach underwent surgery to remove
bone spurs from the elbow. ==Personal life==