In The Knyvett Letters, Thomas was refered to as Knyvett of Middle Temple. He was Sir Thomas Knyvett's uncle Henry's son and was Sir Thomas's barrister in his Chancery suit, who caused him many problems due to his incompetence.

He was admitted to The Middle Temple, June 15, 1608 and Called to the Bar, October 27, 1615, which was subsequently confirmed February 3, 1616.

Thomas Knyvett, (also spelt Knivett, and Knevet), Esq. married Mary Lusher, widow of Richard Lusher, (died 1615), daughter of George Scott, Esq., December 9, 1622 at Saint James, Clerkenwell, London. Mary died in 1623. Her tomb is in The Chancel of Putney Church.

He succeeded to the Office of Clerk of the Parliaments in September, 1635.

National Archives (UK)
Reference: KNY 484 372 x 1
Declaration
By Thomas Knyvett that he would pay the whole of £102.10.0 in which he and Henry Elsyng were bound to his mother Lady Knyvett, Elsyng being bound to pay him £52, (1625).

Reference: D3155/6616
Wm. Duke of Richmond, Summy, esq., Rich. Scott of St. Giles, esq. and George Scott of Great Eyston, Essex of 1st part, Mary Lusher of St. James, Clerkenwell, widow of 2nd part and Thomas Knyvett of the Middle Temple, esq. of 3rd part: settlement of the Manor of Stapleford Tawney and lands in Essex - on marriage of Mary Lusher with Thomas Knyvett. W: Wm. Lusher. W. Tias, Thomas Payne, Jo. Baron, John Plumer, Isaac Hawkins, (December 5, 1622).

Parliamentary Records (UK)
Reference: HL/PO/JO/10/4/2
(1) Order from the King for a copy of the order etc., of House of Lords touching peers answering on honour, February 11, 1636
(2) Copy of the order of the House of May 6, 1628, in pursuance of preceding. Certified by Thomas Knyvett, Clerk of the Parliaments, February 10, 1636. These orders relate to a draft report from the committee for Privileges, that peers should answer only upon honour, and not upon oath, (December 31, 1640).