N M Rothschild & Sons entered the 1950s under the direction of Anthony de Rothschild. After the war, the British and French banks committed themselves to further developing their new operation in the United States, which was eventually to become Rothschild Inc., and increased focus on mergers and acquisitions and asset management. In the 1950s, the firm outgrew its New Court headquarters and took additional premises in nearby Chetwynd House. Although they withdrew from the business of refining bullion in 1967, with the sale of the Royal Mint Refinery to Engelhardt industries, the Rothschilds continued their role as leading international bullion dealers, having chaired the London gold fixing since its introduction in 1919.
The transformation of the bank's activities over this period was accompanied by a change in the bank's management structure. The first non-Rothschild partner, David Colville, was appointed in 1960. In 1961, the Senior Partnership passed to Edmund de Rothschild (1916-2007). Having joined the family bank in 1939, Mr Eddy, as he was known by the staff, had become its effective head in 1955, when his uncle Anthony suffered a severe stroke. From 1952, his chief preoccupation was with what was then the most costly project ever undertaken by private enterprise: the development of the vast hydroelectric potential of the Hamilton (later Churchill) Falls in Labrador. N M Rothschild & Sons was one of the first British banks to resume business contact with Japan after the war, handling some London accounts for the Japanese Ministry of Finance. In 1962, Edmund de Rothschild (1916-2009) was a leading member of City of London missions to strengthen commercial ties with Japan.
Edmund de Rothschild presided over the bank's transition from a highly conservative family firm to a modern institution, and it was under his leadership that in 1962, at the suggestion of Evelyn (later Sir Evelyn) de Rothschild (1931-2022), the bold decision was taken to rebuild New Court, with a building more fitting for the age of the "white heat of technology". Designed by Fitzroy Robinson and Partners, the six storey glass and steel building on the site of the old New Court incorporated features from the 1865 building such as cobblestones from the courtyard and panelling from the Partners’ and Managers’ rooms. When it was completed in 1965, the building was much admired when compared to other City offices being constructed at the time. The third floor consisted of offices occupied by Partners and Senior Managers, and offered new views of the dome of St. Stephen Walbrook. The staff of the firm now numbered over 300.