On 6 June 1949, the art historian and Byzantinologist Marinos Kalligas (1906-1985) took over as the National Gallery’s director, remaining in this post until 2 May 1971. During his tenure, the museum entered a new phase, in which many of its pressing issues were resolved, or the foundations were laid for them to be solved.

In 1954, Law 2814 ‘On the establishment of a legal entity of public law under the name “National Gallery and Alexandros Soutsos Museum”’ came into force, whereby the Alexandros Soutsos Estate was merged into the National Gallery. With the merger, the supervisory committee was replaced by a seven-member Board of Directors, and substantial financial support was secured, in addition to state funding, which contributed to the acquisition of permanent housing, as well as to the enrichment of the collections and the library.

Since 1952 and for at least four years, the National Gallery was housed on two floors on 11, Kolokotroni Street, formerly housing the Ministry of Merchant Marine. Subsequently, both the administration and artworks moved to the Artillery barracks at the corner of Rizari Street and Vassilissis Sofias Avenue. In 1956, however, a competition had been launched for the construction of a building. After many delays and complications related to plot location, construction of the first of the current buildings began, on 26 November 1964. It was completed in 1968, and the first exhibition with works from the collections was inaugurated on 14 May 1970. Meanwhile, in 1968, the National Gallery had once again been forced to move, this time to an apartment at the corner of Efroniou Street and Vassileos Alexandrou Avenue. The artworks went into storage in the building’s basement.

As regards acquisition of artworks, under Marinos Kalligas the enrichment of the collections became more systematic through both acquisitions and donations; the latter were often the result of the director’s personal encouragement. Thus, the painting collection was enriched with works by both older and younger artists, becoming representative of the most remarkable exponents of all periods and movements. The sculpture collection was augmented, providing a more complete overview of the Ionian sculptors until the modern era; the engraving collection received high-quality prints, including by French artists as well as Rembrandt, Pieter Bruegel the Elder, Dürer, and Goya. In addition, on a voluntary-work basis, artworks were catalogued, and the archives were organised.

Until the housing issue was resolved, a temporary solution was provided for public display of art between 1953-1959, by organising exhibitions from the Gallery's collections at the Zappeion Hall. To accompany these exhibitions, small yet quite detailed catalogues were published (1953, 1954, 1955/1, 1955/2, 1956, 1957) the first ones to follow those published by Georgios Iakovidis in 1906 and 1915. Temporary exhibitions were also organised, including a selection from Stavros Niarchos’ collection in 1958, as well as exhibitions from the collections of the National Gallery in other cities (1955, 1962/1, 1962/2).