He was the son and heir of John Knyvet (1358/9–1418) by his first wife Joan Boutetout (d.c.1417), daughter and heiress of Sir John Boutetout (d. by 1377) of Mendlesham by his wife Katherine.[1][2]
By 1412 he had married Elizabeth (d.1441), daughter of Constantine, 2nd Lord Clifton (1372–95) of Buckenharn Castle, Norfolk by his wife Margaret, sister of Sir John Howard[1] and daughter of Sir Robert Howard (d.1389) of Wiggenhall and East Winch,[3] and heiress of her brother Sir John Clifton (d.s.p. 1447).[1]
His ancestral home of Southwick was inherited by his daughter, Joan, and her husband, John Lynne (d.1486/7). The rest of his property was inherited by his son and heir of the same name, John. He had married in August 1430, Alice Lynne, the sister of his sister Joan's husband John Lynne.[1] John Knyvet and Alice Lynne were the parents of Sir William Knyvett (d.1515).
^C. Rawcliffe, 'Knyvet, John (1358/9-1418), of Mendlesham, Suff.', in J.S. Roskell, L. Clark and C. Rawcliffe (eds), The History of Parliament: the House of Commons 1386-1421 (from Boydell and Brewer, 1993), History of Parliament Online.