His first major work, the emergency cité de transit Djenan el-Hassan (1956-8), reflected his concern with the eradication of slum housing; its cellular construction, with individual vaulted roofs, echoed local vernacular architectural forms.
After the War of Independence, Simounet moved to Paris (1963), but many of his works continued to address the problems of design for warm climates through the suitable expression of materials, massing and openings; examples include the student housing (1962–70) for the University of Tananarive, Madagascar, and a series of holiday homes in Corsica.
His new buildings for the Musee de la Prehistoire de l'Ile-de-France (1975-9), Nemours, and the Musee d'Art Moderne du Nord (1978–83), Villeneuve d'Ascq, reveal a careful orchestration of natural lighting and details to enhance the individual display of works of art.
He also won the limited competition for the conversion of the 17th-century Hôtel Salé in the Marais district of Paris into the Musée Picasso (1976–85); the austere and luminous quality of the white-washed walls and pristine volumes was generally acknowledged to be the perfect showcase for Picasso's personal collection.
In Saint-Denis he designed some low-cost housing (1983) in the shadow of the abbey; arranged around small courtyards, it alluded to the historic fortifications.