Gaumy was born in Pontaillac, Charente-Maritime, France. He attended school in Toulouse and Aurillac and went to university in Rouen. While a student in Rouen, he began working as a freelance photographer to help pay for his education. In 1973 he joined Gamma (agency).
Much of his work has focused on human confinement. In 1975 he began work on two such projects in France: L’hôpital and Les Incarcérés, both of which were published as books. Les Incarcérés was an unprecedented project on French prisons—he was the first to receive permission to photograph them. In 1984 he made his first film, La Boucane. It was nominated for a César in 1986. That year he also began a series of trips aboard trawlers which led to his 2001 publication Pleine Mer. Beginning in 1987 he spent two years documenting Octeville-sur-Mer through the eyes of the so-called village idiot Jean-Jacques. Since the late 1980s he has also traveled often to Iran and has also traveled in Central America and Africa 
He has made several other films. In recent years he has been documenting life on a nuclear submarine and has also worked on a series of mountain landscapes.Retrospettive.
In mare aperto. Iran.