Born in Basel, Switzerland, he studied zoology at the University of Basel and worked later in Geneva, Munich, Paris and Berlin, but mainly in marine biology laboratories in France (Banyuls-sur-Mer, Roscoff, Villefranche-sur-Mer) and Helgoland.
Valtat suffered from tuberculosis, and he spent many autumn/winter seasons along the Mediterranean coast in Banyuls, Antheor and Saint-Tropez.
He won a scholarship to France in 1939 and worked at the National Museum of Natural History in Paris, the Oceanographic Museum of Monaco, at the Marine Biological Stations at Banyuls-sur-Mer and at Roscoff.
Aided by tax benefits, natural sweet wines such as Banyuls, Muscat de Frontignan, and Rivesaltes superseded Byrrh, which went out of fashion.