Sir John Thynne (c. 1515 – 21 May 1580) was the steward to Edward Seymour, 1st Duke of Somerset (c. 1506 – 1552), and a member of parliament.

His uncle William Thynne was a courtier in the household of King Henry VIII and a literary editor.

[1] Before he had long been Seymour's steward, Thynne began to build up his own estates in the west of England and Oxfordshire.

[2] His greatest prize was the former Carthusian Longleat Priory, together with land in three parishes on the borders of Wiltshire and Somerset, which he bought on his own account in 1540.

Other possessions of the former priories of Longleat and Hinton Charterhouse were granted by the Crown to Seymour, who sold them to his steward Thynne on 25 June 1541.

After Somerset's execution, like his other followers who were spared, Thynne lost his offices and much of his land,[2] and he was heavily fined.

[2] When Queen Elizabeth I inherited the throne, many of Thynne's friends returned to power, and he was again able to expand his estates[1] and to recover some of his offices.

[2] When he died in 1580, Thynne left manors in Wiltshire, Gloucestershire, Somerset and Oxfordshire, and property in the cities of London, Westminster, and Bristol.

The house was unfinished when Seymour fell from power, but a correspondence survives, dated between November 1548 and June 1549, which shows Thynne directing the plans.

[1] At Longleat, Thynne took thirty-seven years to design and build his own great neo-classical house with four facades, Doric, Ionic, and Corinthian pilasters, and regularly spaced bay windows.