In 1873 Ascott, together with 90 acres of land, was bought by Baron Mayer de Rothschild whose seat was at Mentmore, three miles away. The following year Leopold de Rothschild took over Ascott as a hunting box. During the following years the house was transformed and enlarged to form a family home.

The nucleus of the remarkable collection of works of art at Ascott, more particularly the French furniture and most of the pictures, was inherited in the late 19th century by Leopold de Rothschild from his father, Baron Lionel de Rothschild.

The collection was further enhanced by Anthony de Rothschild (1887-1961) who added English furniture, paintings and a remarkable collection of over 400 pieces of Chinese ceramics. The three colour wares central to the collection make it amongst the foremost in the world.

From 1941-1947 a group of Chelsea Pensioners lived at Ascott after the Royal Hospital, Chelsea was bombed.

In 1949 the Ascott Collection, together with the House, its grounds of 261 acres and an endowment were given to the National Trust by Anthony de Rothschild.

 
The garden at Ascott has always been among its best known and more original features. Leopold de Rothschild was a talented gardener who laid out the grounds of Ascott with the assistance of Sir Harry Veitch, the famous Chelsea nurseryman.

The gardens were a mixture of the formal and informal including the exuberant Venus and Cupid fountains by Thomas Waldo Story. Leopold's Head Gardener, John Jennings, worked at Ascott for 30 years.

The main part of the garden was laid out in the 1902 following Leopold's marriage and was conceived partly as a present for his wife and also as a celebration of their happy marriage. As shown in the motto round the topiary sundial 'Light and shade by turn, but love always'.

 
George Devey, the architect working on the house, was interested in garden design and played a significant role in the revival of 'Old English' formal gardening. His architectural work in the garden included the Tea House at the east end of the Madeira Walk and the Skating Hut overlooking the Lily Pond.

After the Second World War the more elaborate Victorian bedding out was reduced, some of the topiary removed and many flowering trees added to the garden.