Renovations were undertaken during the tenures of the Guise and Gambier-Parry families, with the latter also including extensive development of the grounds.

[5] The manor underwent improvements of its interior in the 18th century for owner Sir John Guise, 1st Baronet, the son of one of Dennis Cooke's sisters.

Further alterations were made in the early 19th century for his son and successor, Sir Berkeley William Guise, 2nd Baronet.

[1] Thomas Gambier-Parry died in 1888; his widowed second wife Ethelinda Lear retained the manor until her demise in 1896.

[5][11] She was succeeded by her husband's son, the youngest child of his first marriage, composer Sir Charles Hubert Hastings Parry.

[5][12][13] During the Second World War, Highnam Court was commissioned on 28 April 1941 as an overspill centre for navy recruits, and defined as a tender to HMS Ganges.

[13] Before his death in 2010, Fenton gave documents related to the administration of the estate, covering the period from 1650 to 1940, to the Gloucestershire Archives.

[13][16] Ownership of the manor was transferred in 1977; Gloucester businessman Roger Head later became the owner of Highnam Court in 1994, serving as High Sheriff in 2015–16.

However, when Thomas Gambier-Parry purchased the estate in 1838, he reversed the functions of the south and north sides of the house.

His alteration of the layout resulted in the south side of the manor having unobstructed views of the gardens and adjacent lake.

The nine-window, symmetric south facade is two and a half storeys and features a five-window, slightly recessed centre section.

It is believed that the statue of Oliver Cromwell as Hercules that is in the alcove in the east garden was originally in the niche.

The plaster ceiling has figures of a lion, eagle, dolphin, and phoenix at the corners of the room, and is an example of the "fine rococo plasterwork" in the house.

[1] In the 18th century, Sir John Guise not only made improvements to the interior of Highnam Court; he also landscaped the grounds.

The grade II listed south terrace was the work of architect Vulliamy in 1843, and includes a balustrade, urns, and steps.

[3] Thomas Gambier-Parry began to lay out his gardens in 1840 with the assistance of James Pulham and, less than four decades later, they were among the loveliest in the United Kingdom.

[3][24][29] The orangery knot garden to the west of the house was finished in December 2004, and includes variegated boxwood hedging and a statue of Mercury, the Winged Messenger.