Growing up in Switzerland, Poncet was surrounded by artists, his father was a painter and his grandfather was the famous Nabis artist Maurice Denis. At the age of fourteen he went to study under the sculptor Germaine Richier in Zurich. From 1942-1945 he attended the École des Beaux Arts in Lausanne, after which he moved to Paris where he took a studio and enrolled at the Académie de la Grande Chaumière.