Cros was a well regarded poet and humorous writer. He developed various improved methods of photography including an early color photo process. He also invented improvements in telegraph technology.
He is perhaps most famous as the man who almost, but not quite, invented the phonograph. In April 1877 he submitted a paper to the Academy of Sciences in Paris suggesting that the vibrations of sound waves could be traced with a pen attached to a vibrating membrane, then the waves could be engraved into metal, and then a stylus attached to a membrane could be run over the engraved wave to reproduce the sound. Before Cros had a chance to follow up on this idea or attempt to construct a working model, Thomas Alva Edison introduced his first working phonograph in the USA. Edison and Cros apparently did not know of each other's work in advance.
Charles Cros died in Paris.