Clavel was born in Lons-le-Saunier. From a humble background, he was largely self-educated. He began working as a pastry cook apprentice when he was 14 years old. He later had several jobs until he began working as a journalist in the 1950s. After the war, he worked for the social insurance, and he could not dedicate himself to literature until 1964. He has lived and worked in many places and lived in Savoy until his death.
His first novel was L'Ouvrier de la nuit (Night Worker, 1956). He later published works for young people and numerous novels, at times organised into series: La grande patience (The Great Patience, 4 volumes -- 1962-1968), Les Colonnes du ciel (Heaven's Pillars, 5 volumes -- 1976-1981), or Le Royaume du nord (Northern Kingdom, 6 volumes -- 1983-1989).
In his writings, he employed simple language and attached importance to humble characters and to the defence of humanist values by questioning violence and war.
He died in Grenoble.