Thomas Knyvet was the son and heir of John Knyvet, of Plumpstead, Norfolk, and his wife, Agnes, daughter of Sir John Harcourt, of Stanton Harcourt, Oxfordshire. Jane Knyvet, his paternal grandmother, was the second and only surviving daughter of Sir John Bourchier, 2nd Lord Berners (1467-1533), a descendant of King Edward III, and one of King Henry VIII's most trusted courtiers. On the death of the 2nd Lord Berners she succeeded as de jure Baroness Berners, and on her death in 1561/2 Thomas Knyvet succeeded her as de jure 4th Baron Berners and inherited the estate of Aswellthorpe in Norfolk. Knyvet was knighted by Queen Elizabeth I in her progress to Norfolk in 1578, and the following year was appointed High Sheriff of Norfolk. He married Muriel, daughter of Sir Thomas Parry, Master of the Court of Wards and Liveries, and Treasurer of the Household to Queen Elizabeth I. In 1616 he obtained a certificate from the commissioner of the office of the Earl Marshall of his 'right and title to the Barony of Berners', but he died shortly afterwards, before obtaining the King's confirmation. He was buried at Ashwellthorpe and was succeeded by his grandson Thomas.
Both stylistically and on the basis of the sitter's costume, this portrait would appear to date from the mid-to-late 1560s when Sir Thomas Knyvett was in his late twenties. An attribution to the Netherlandish artist Steven Van Der Meulen has previously been suggested but the relatively recent discovery of the artists's will, written on 5 October 1563 during a plague epidemic, and proved on 20 January 1564, makes this unlikely (see Dynasties, Painting in Tudor and Jacobean England 1530-1630, catalogue to the exhibition at the Tate Gallery, London, 1995-6, ed. K. Hearn, under no. 47). A portrait of the sitter's great grandfather, John Bourchier, 2nd Baron Berners, attributed to Ambrosius Benson, was included in the Dynasties exhibition (see exhibition catalogue, op.cit., no.3, illustrated).