Takuya Onishi was certified as an astronaut by the Japan Aerospace Exploration Agency (JAXA) in 2011. He has spent approximately 259 days in space, serving as a Flight Engineer aboard the International Space Station (ISS) during Expeditions 48, 49, and 72, and as the ISS Commander during Expedition 73 in 2025.

In addition to his missions in space, he has also served as a JAXA Flight Director since 2020, supporting mission control operations for the Japanese Experiment Module "Kibo." Serving as both a Flight Director and an astronaut is an unprecedented achievement at JAXA.

Drawing on his extensive knowledge of ISS operations, he was appointed as the third Japanese commander of the ISS. During his most recent stay aboard the station, he conducted a wide range of Japanese and international scientific experiments that took advantage of the unique microgravity environment of space.