Poncet studied law at the University of Geneva . After internships in Geneva, Zurich, London and Washington DC, he was admitted to the bar in 1972. From 1975 worked in the family's law firm Poncet, Turrettini, Amaudruz & Neyroud, and later at Lalive Budin. He received his doctorate in Geneva. In 1986,
Poncet his own law firm Ziegler Poncet Grumbach ZPG today Carrard Lüscher. He is a specialist in international affairs and arbitration. He has long been active in international arbitration, first as secretary and subsequently as an arbitrator, chairman or adviser. Poncet is the author of numerous legal publications.
Poncet sat from 1989 to 1996 for the Liberal Party in the National Council and the Grand Council of the Canton of Geneva .