[4][5] Schwärzler reached the final of the 2023 US Open – Boys' doubles alongside partner Federico Bondioli where they lost to Max Dahlin and Oliver Ojakäär despite twice having a match point.

[10] At the 2024 French Open, Schwärzler won his first junior Grand Slam title in the boys' doubles, partnering with Nicolai Budkov Kjær.

[11] In May , Schwärzler won his first ATP Challenger Tour title at the 2024 Macedonian Open in Skopje, defeating Sergey Fomin, Ergi Kırkın, Andrew Paulson, Gerard Campana Lee and Kamil Majchrzak in the process.

João Fonseca, Schwärzler, Rei Sakamoto, Gabriel Debru and Learner Tien became the youngest champions of 2024 at that level.

[12][13][14] Schwärzler made his ATP debut at the 2024 Generali Open Kitzbühel, losing to Thiago Seyboth Wild in the first round.