Clervoy was born in Longeville-lès-Metz, France. He has a twin brother, Patrick, a military physician. He joined the French Air Force, where he trained as a test pilot. He was selected as an spationaut candidate by France in 1985 and trained extensively at the Russian Star City before being named to the European Space Agency's astronaut corps in 1992. He has flown on three space shuttle flights as a mission specialist, including STS-66 (1994), STS-84 (1997) and as flight engineer on STS-103 (1999), a Hubble Space Telescope repair mission.