Firmin Mattis had limited skiing experience at the end of World War II, but came to be trained by Olympic champion Henri Oreiller. This led to Mattis being selected to represent France at the 1952 Oslo Olympics, where he was 12th in the slalom. He then took part in the 1954 World Championships, where he was again 12th in the slalom, and then became the first person to win the Critérium de la Première neige the following year. He sustained an injury prior to the 1956 Cortina d’Ampezzo Olympics that ended his competitive career, but he later worked as a coach.