The third and final design for the UNESCO Headquarters was approved by the General Assembly on July 1, 1953. Breuer, Bernard Zehrfuss and Pier Luigi Nervi designed another complex of three buildings. A square concrete-frame building housed space for the permanent delegations. Its concrete ground floor supported four glazed stories, and as Isabelle Hyman has pointed out, it appeared to be a scaled-down version of the tower from the earlier Porte Maillot scheme. The Y-shaped Secretariat featured glass facades with elaborate sun-shade mechanisms. The massive, sculptural concrete pilotis, which supported the upper stories, framed the ground floor corridors. Soaring concrete canopies designed by Nervi marked the north and south entrances. The building's curved facade completed the semi-circle of the Place de Fontenoy. The final building was the Conference Hall. Working closely with Nervi, Breuer designed a concrete-shell building with folded walls and roof connected to the Secretariat by a low rectangular element. Critics such as Lewis Mumford praised the bold form of the Conference building but criticized the design of the Secretariat, as well as the failure of the latter building's sunshades to control the build-up of heat within the offices.

Painting and sculpture were an important component of the design, and after a somewhat contentious selection process, six artists were awarded commissions. Pablo Picasso painted a mural called "The Fall of Icarus" for the lobby of the Conference building, while Joan Miró created two murals of hand-painted ceramic tiles, "The Wall of the Sun" and "The Wall of the Moon" for exterior walls located at the eastern edge of the piazza. Henry Moore produced a monumental sculpture, entitled "Reclining Figure." Jean Arp designed a bronze relief ("Constellation") for the end wall of the library. Isamu Noguchi designed a garden organized around modernist sculptures. Finally, Breuer's friend, Alexander Calder contributed a mobile named "The Spiral."