Sir James Thynne (1605 – 12 October 1670) was an English landowner and politician who sat in the House of Commons in two periods between 1640 and 1670.
Thynne was the eldest son of Sir Thomas Thynne, of Longleat, Wiltshire. He was knighted at Berwick on 23 June 1639.
In November 1640, Thynne was elected Member of Parliament for Wiltshire in the Long Parliament. He was disabled from sitting in 1642.
In 1655 Thynne founded an almshouse at Longbridge Deverill. Following the Restoration, he was High Sheriff of Wiltshire in 1661. Sir Christopher Wren advised him on improvements to the house at Longleat which included the great stairs and stone terrace. In 1664 he was re-elected MP for Wiltshire in the Cavalier Parliament and sat until his death in 1670.
Thynne married Lady Isabella Rich, daughter of Henry Rich, 1st Earl of Holland and his wife Isabel Cope. He died without issue and his nephew Thomas succeeded to the estates.