Originally the site of a fortified manor licensed in 1332, the present building is not actually a castle, but was built in the 1720s as an almost exact copy of Palladio's Villa Rotunda. It was designed in 1723 by Colen Campbell who had been commissioned by John Fane, 7th Earl of Westmorland. The interior features plasterwork by Giovanni Bagutti and fresco painting by Francesco Sleter. The house is situated in a landscaped park and valley with a number of surrounding pavilions and lodges which are also Grade I listed.
The house passed through descent to Barons Oranmore and Browne whose family seat it became. It was sold in 1930  and used as a prisoner of war camp during World War II. In the 1950s and 1960s it was owned by Michael Lambert Tree, a son of Ronald Tree and an heir to the Marshall Field mercantile fortune, and his wife, the former Lady Anne Cavendish, a daughter of the 10th Duke of Devonshire.
Mereworth Castle is owned by Mahdi Al-Tajir, the former United Arab Emirates ambassador to the United Kingdom and owner of the Highland Spring bottled water company, who purchased it in 1976 for $1.2 million. It is not generally accessible to the public, but does open on rare occasions for guided tours.
- "Mereworth Castle (main block) with moat walls to north, Maidstone Road (south side), Mereworth, Tonbridge and Malling, Kent". English Heritage. Retrieved 2008-05-20. This source attributes the plasterwork to Francesco Bagutti, but Giovanni Bagutti would appear to be more likely.
- 5 houses have been built in Britain based on Palladio's Villa Rotunda (the others being Nuthall Temple, Nottinghamshire [demolished]; Henbury Hall, Cheshire; Chiswick House, Greater London; and Foots Cray Place, Kent [demolished])
- "The Peerage". The Peerage. Retrieved 2012-02-16.
- "Images of England, Pavilion to the North East of Mereworth Castle, Maidstone Road (south side), MEREWORTH, Tonbridge and Malling, Kent". English Heritage. Retrieved 2008-05-20.
- "Pavilion to the North West and Stables of Mereworth Castle, Maidstone Road (south side), MEREWORTH, Tonbridge and Malling, Kent". English Heritage. Retrieved 2008-05-20.
- Lord Oranmore and Browne's obituary Telegraph
- "Island farm". Islandfarm.fsnet.co.uk. Retrieved 2012-02-16.
- Watermills of the East Malling and Wateringbury Streams, Part 2, Chapter 1
- Watermills (Kent and the Borders of Sussex) p134.
- "Sunday Times Rich List 2010: Britain's richest see wealth rise by one third". The Daily Telegraph. 24 April 2010.
- Monday, Aug. 02, 1976 (1976-08-02). "BRITAIN: Dinner for 370,000, Please, James". TIME. Retrieved 2012-02-16.
- Stutchbury, Howard, The Architecture of Colin Campbell, Harvard University Press, 1967, 54-58. ISBN 0-674-04400-2
- Harris, John, The Palladians, Trefoil Publications Ltd, 1981, 66-67. ISBN 0-86294-000-1
- Country Life, XLVII, 808,876,912; XCV, 242; CIV,728; CXVI, 209
- Fuller, Michael (1980). The Watermills of the East Malling and Wateringbury Streams. Maidstone: Christine Swift.
- Fuller & Spain (1986). Watermills (Kent and the Borders of Sussex). Maidstone: Kent Archaeological Society. p. 134. ISBN 0-906746-08-6.
- Images of England website including a description for listing purposes
- The DiCamillo Companion to British & Irish Country Houses
- York University website entry
- 1930s photographs