He was born in Nîmes and trained as an engineer. He became interested in astronomy and comets in particular, observing the return of what would later be named Comet Encke. He later made a very complete calculation of the orbital elements of another comet, for which he won recognition.
He built a private observatory at his home and when he went to take up a post as director of the Marseille Observatory, he left his home to a young man named "A. Laurent", who used the observatory to discover the asteroid 51 Nemausa. The house, at 32 rue Nationale in Nîmes, has a plaque commemorating the discovery. 
Valz himself was at one time said to be the discoverer of two asteroids, 20 Massalia and 25 Phocaea, but nowadays these are credited to the Italian astronomer Annibale de Gasparis and to Valz's colleague Jean Chacornac, respectively.