After winning the boys' singles title at the 2024 French Open, he reached a career high ITF junior combined ranking of No.

[4] In January 2024, he signed a letter of intent to play tennis at the University of California, Los Angeles.

[5][6] Bigun represented the United States at the 2022 Junior Davis Cup in Antalya, reaching the final.

In 2024, at the Australian Open, he reached the quarterfinals in singles and the semifinals in doubles with partner Jagger Leach.

[8][9] Bigun became the first American player to win the junior boys' singles title since Tommy Paul in 2015.