While being a bank clerk in 1942, Paris-born Roger Masmonteil published his first illustrations in Allô 18, the magazine of the firemen where he fulfilled his military service during the War. Back in civil life, Mas returned to his work at a bank. He eventually found employment as the successor of José Cabrero Arnal on his series 'Gavroche et G. Latine' in Avant-Garde and 'Becdor le Canard' in L'Humanité. In addition, Mas illustrated 'Barbichette', created with a script by Jean-Claude, also in L'Humanité.
When Arnal got ill, Mas succeeded him on the daily 'Pif le Chien' strip in L'Humanité. Starting in 1954, he also drew the 'Pif' comic that appeared in the magazine Vaillant. In addition, he created the 'Spoutnik' comic for Pif Mensuel and L'Humanité from 1955 to 1965. As the lead artist of 'Pif le Chien', Mas created 'Pifou', Pif's son who got his own series and even his own pocket book after a while.
In 1967 Roger Mas left the 'Pif' comic in Vaillant to continue 'Pifou' and to create his own series, 'Léo Bète à Part' with Jean Sanitas in Pif Gadget, the successor of Vaillant magazine. In 1968 and 1969, Mas had a brief appearance in Tintin with 'Késako'. Starting in 1987, R. Mas illustrated new stories with 'Pifou' for an eponymous monthly.