In October 2018, Hijikata won silver at the Tennis at the 2018 Summer Youth Olympics – Boys' doubles, teaming with Bulgaria's Adrian Andreev.

Later that year, in September, Hijikata won his first professional singles title at the M15 Fayetteville, in Arkansas, United States.

In January 2022, Hijikata made his ATP tour debut at the 2022 Melbourne Summer Set 1 after qualifying for the main draw.

[12] In August, he qualified for the 2022 Los Cabos Open and reached the round of 16 recording his first ATP win after the retirement of the Mexican wildcard debutant Rodrigo Pacheco Méndez.

He became the youngest Australian to win a Challenger title since 2018, when the-then 19-year-old Alexei Popyrin won in Jinan, China.

[14] Hijikata was given a wildcard into the Australian Open, where he recorded his first Grand Slam win by defeating Yannick Hanfmann in a come-from-behind victory.

1 doubles pair Wesley Koolhof and Neal Skupski in the quarterfinals,[18] and eighth seeds Marcel Granollers and Horacio Zeballos in the semifinals.

[21][22] At the 2023 Delray Beach Open he reached the semifinals in doubles partnering American Reese Stalder and defeating second seeded pair of Jamie Murray and Michael Venus in the quarterfinals.

He made his Masters 1000 debut in Indian Wells as a qualifier, and defeated Mikael Ymer in the first round in straight sets.

[28][29] He reached the fourth round of the 2023 US Open having received a wildcard, defeating Pavel Kotov, Márton Fucsovics[30] and Zhang Zhizhen.

At the 2024 Dallas Open, Hijikata made it to his fourth doubles final alongside William Blumberg, losing to Max Purcell and Jordan Thompson.

[40] He reached his third ATP quarterfinal at the 2024 Delray Beach Open a defeat over Liam Broady and an upset over sixth seed Matteo Arnaldi.

At the 2024 Queen's Club Championships, where he made his ATP 500 main draw debut as a qualifier, he defeated Frances Tiafoe by retirement and Matteo Arnaldi to reach his second grass court quarterfinal.