Thynne first made his mark in May 1594, at the age of sixteen, when he clandestinely married Maria (or Mary) Touchet, also sixteen, a gentlewoman at the court of Queen Elizabeth and a daughter of Lord Audley. The two were married on the day they first met and for some time kept their marriage secret because their fathers were bitterly opposed to each other. When their story became known, Thynne's father, John Thynne the Younger, tried unsuccessfully to have the marriage annulled. The story is said to have contributed to the inspiration for Shakespeare's Romeo and Juliet. With Maria, Thynne had three sons, before his wife died in childbirth. Two of these sons survived childhood, James Thynne (died 1670) and Sir Thomas Thynne.
Maria's surviving correspondence between 1595 and 1611 was published by the Wiltshire Record Society in 1983 under the title Two Elizabethan Women: correspondence of Joan and Maria Thynne. After the death of Maria in 1611, Thynne married secondly Catherine Howard, a daughter of Hon. Charles Howard, son of the first Viscount Howard and niece of Lord Howard of Bindon. With her he had further sons, including Sir Henry Frederick Thynne, 1st Baronet (1615–1680), ancestor of the Marquesses of Bath.
In 1601 Thynne was elected Member of Parliament for Hindon. He was re-elected MP for Hindon in 1604. In the same year, he succeeded his father to the family estates and on his father's death he had himself returned at a by-election for the county of Wiltshire. However, this election was disallowed by the Commons on the grounds that a sitting member was not eligible to be returned for a second constituency. Thynne was High Sheriff of Wiltshire for 1607–08. In 1621 he was elected for MP Heytesbury and was re-elected MP for Heytesbury in 1624. He was elected MP for Hindon again in 1625 and was re-elected MP for Hindon in 1626 and 1628.
Among the estates Thynne inherited was one at Kempsford in Gloucestershire, where he built a new country house, demolishing an important fortified manor house which since the 13th century had defended a crossing of the River Thames.
Thynne died on 1 August 1639.
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- Sir Thomas Thynne at thepeerage.com, accessed 7 July 2011
- David Booy, Personal disclosures: an anthology of self-writings from the seventeenth century (2002), p. 41: "Maria Touchet (c. 1578–1611), the daughter of Lord Audley, married Thomas Thynne, the heir to Longleat, on the day she first met him, 16 May 1594. They were both 16."
- Cathy Hartley (15 April 2013). A Historical Dictionary of British Women. Routledge. p. 428. ISBN 978-1-135-35533-3.
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- Richard K. Evans, The Ancestry of Diana, Princess of Wales, for twelve generations (New England Historic Genealogical Society, 2007): "Nr. 4152: Sir Thomas Thynne, M.P. 1601, 1604, 1621, 1624, 1625, 1626 and 1628, Sheriff of Wiltshire 1607–8, etc, born ca. 1578 and died 1 August 1639."
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|Parliament of England|
| Member of Parliament for Hindon
With: Sir George Paule 1601
Sir Edmund Ludlow
Sir Edmund Ludlow
Sir Edwin Sandys
Sir Henry Ludlow
| Member of Parliament for Heytesbury
With: Sir Henry Ludlow
Sir Charles Berkeley
| Member of Parliament for Hindon
With: William Lambert 1625
Thomas Lambert 1626
Lawrence Hyde 1628–1629
Parliament suspended until 1640