Doi holds a doctorate from the University of Tokyo in aerospace engineering, and has studied and published in the fields of propulsion systems and microgravity technology.

Doi flew as a mission specialist aboard STS-87 in 1997, during which he became the first Japanese astronaut to conduct a spacewalk.

Takao Doi visited the International Space Station in March 2008 as a member of the STS-123 crew.

STS-123 delivered the first module of the Japanese laboratory, Kibō, and the Canadian Dextre robot to the space station.

During this mission, he became the first person to throw a boomerang in space that had been specifically designed for use in microgravity during spaceflight.