He was a foreman and engineer at the Energiya Rocket and Space Complex from 1984 to 1986, supporting crew training aboard the Russian space station Mir. Treschev was selected as a cosmonaut in 1992, and flew on Endeavour on 5 June 2002 to the International Space Station as a member of the fifth resident crew. He remained there for six months, performing one space walk to install various devices, including a frame to house components for future space walks.