Spiro obtained his PhD from University of Paris-Sud, Orsay in 1976. His early research in particle physics led him, as a member of the UA1 experiment, to participate in the discovery of the intermediate bosons W and Z. He then turned to study particles from the cosmos by participating in the GALLEX solar neutrino detection experiment. He became then the spokesperson of the microlensing search experiment EROS (Experience de Recherche d'Objets Sombres).