Guédon was an officer from the tirailleurs (a skirmishing unit) who had graduated from the Saint-Cyr military academy and had fought in the Rif.
He made the acquaintance of Henri Frenay at some point during military school where he became a specialist of the 4th Bureau.
Leader of a company of the French 13th motorized infantry, he was wounded by a bomb explosion at the start of the German offensive.
In collaboration with Frenay and Lieutenant Pierre de Froment, Guédon organised the Libération Nationale information and propaganda movement.
Assigned as an instructor in a staff school, he subsequently entered the commissariat of prisoners and deportees, where Frenay charged him with organizing the future repatriation of French nationals held in Germany.