Marion was born in Marseille, and entered the École Polytechnique at just 18 years of age.
He then became managing director of aerospace manufacturer Aerospatiale's North American operations for ten years.
[1] In 1981, Marion was asked by his friend, Charles Hernu (who had been made Minister of Defence in François Mitterrand's government), if he would become director of the SDECE, the French external intelligence agency.
He agreed, and set about modernising the service, reducing its ties to the French military, and changing its name to DGSE.
Marion clashed with Mitterrand over several issues, including the creation of an anti-terrorist cell operating from within the President's office, and in 1982 he was replaced by Admiral Pierre Lacoste.