It was the acquisition by the State in 1959 and 1963 of the Jean Walter and Paul Guillaume collection, subject to usufruct, which gave the Musée de l'Orangerie its definitive appearance. Indeed, Domenica Walter (1898-1977), the widow of the art dealer Paul Guillaume (1891-1934) and then of the architect and industrialist Jean Walter (1883-1957), fulfilled her first husband's desire to create the "first museum of French modern art" open to the public. The State offered to exhibit the collection at the Orangerie.
A second renovation project was led by the architect Olivier Lahalle from 1960 to 1965. The exhibition galleries were knocked down and two superimposed levels running the entire length were added to the building. A monumental staircase with a banister designed by Raymond Subes (1893-1970) replaced the entrance vestibule to the Water Lilies. It led to a series of salons requested by Domenica to display the 146 paintings. A public presentation of the collection took place in 1966, inaugurated by the Minister of Culture André Malraux. Domenica kept the paintings until her death in 1977.
A third renovation project was carried out from 1978 to 1984 in order to consolidate the building, refurbish the rooms and permanently house the entire collection, named the "Jean Walter and Paul Guillaume collection" according to Domenica's wishes. The Orangerie thus became an independent national museum, separate from the administrative supervision of the Louvre and the Jeu de Paume, whose Impressionist collections were destined for the future Musée d’Orsay.