He became film score composer on two productions respectively released in 1930 (Cendrillon de Paris, with Alibert and Pauline Carton) and 1931 (Les Vagabonds magnifiques, with Nadia Sibirskaïa and Georges Melchior).
His third film was Les Bleus de la marine by Maurice Cammage (1934, music cowritten with Vincent Scotto), starring Fernandel and the screenwriter Jean Manse.
In association with the latter (the actor's stepbrother) as librettist, he composed his third operetta, Ignace, created in Marseille in 1935, then revived at the Théâtre de la Porte-Saint-Martin in Paris in 1936, with Fernandel in the leading role, Andrex, Edmond Castel, Alice Tissot and Henry Trévoux.
There followed a collaboration with Fernandel for twelve other films (to which Jean Manse participated, mostly as lyricist), including Barnabé by Alexander Esway (1938), Simplet (directed by the actor, 1942) and L'Aventure de Cabassou by Gilles Grangier (1946).
Dumas also contributed to eight films without Fernandel, including his first two already mentioned, Pierre et Jean by André Cayatte (1943, with Renée Saint-Cyr and Noël Roquevert) as well as Cécile est morte!