A student at Lycée Thiers in Marseille (Saint-Charles annex),[3] and later a law graduate, Closon was involved in Christian-democratic movements during his youth.
In July 1944 he was appointed Commissaire de la République for Nord and Pas-de-Calais, while Raymond Aubrac was assigned to Marseille.
[4] He was sent on a mission in early August with Charles Luizet, newly appointed Prefect of Police in Paris, and Lazare Rachline.
On their third attempt, Luizet and Closon were dropped in a resistance area near Apt in the Vaucluse on 10 August.
By late August, Closon arrived in Lille and held his post as regional Commissioner of the Republic until 1946.