From 1939 to 1947, he was trained as a painter at the Royal Academy of Fine Arts in Brussels and the Art School of Saint Joost Ten Node.
He painted cityscapes and buildings with a preference for views in Paris, Brussels and Amsterdam. He also painted some North Sea marine works and the occasional interior subject.
Mommaerts was also a talented theater decorator who lectured on theatre and set design in his capacity of professor at the Academy of Fine Arts in Brussels (1963-1983) and at the Academy of Ixelles. He was a fellow of the Godecharle Prize 1947 and co-founder of the Artes Bruxellae Artists' Association (1974).
In 1994-1995 there was a major exhibition of his work in the town Brussels suburb of Schaarbeek.