It was at the Ecole Professionelle de Dessin Industriel (EDPI) (Professional School of Industrial Design) that Mennessons studied History of Art as option. He began to visit museums which had recently re-opened after the war and produced his first works in drawing and painting (1943-44). In 1945 he was an Industrial Designer at the aeronautical armoury at Châtillon-sous-Bagneux. Within the year 1945-1946 he decided to give up a profession leading to a brilliant future and instead to throw himself into the insecurity and adventure of painting.

For him, his art was as much research on an artistic scale as it was a means to find himself philosophically.

Attracted to sculpture, he befriended Henri Laurens (1949) who encouraged him to abandon teaching at the Ecole des Beaux Arts (School of Fine Arts). He was accepted as a student at Saint-Remy by Albert Gleizes and his stay in Provence until Gleizes' death in 1953 is notable for an intense creativity and exhibitions. Fleeing the static and stultifying repetition was the essence of his learning.

On his return to Paris, deprived of a studio he returned to "figuration", the opposite of his leanings under Gleizes. From this, a new method was born, favouring the space between objects, rather than the objects themselves.

In 1960 he finally found a studio and art lovers helped him to live without having to hold a steady job. In these lyrically expressive works the favourite themes - music, sport, the circus, the sunlight on the Dordogne, spirituality - all come together in a composition which move around its core; this, at first, very busy gradually giving way to an "empty fullness". His works are presented in several personal and joint exhibitions; the last in 1965 resulting in the French State purchasing one of his canvases.