Kynaston was the youngest son of Sir Roger Kynaston (c. 1432/1433–1495), High Sheriff of Shropshire, who was thought to have killed Lord Audley at the Battle of Blore Heath, and Roger's second wife, Lady Elizabeth Grey, daughter of Henry Grey, 2nd Earl of Tankerville and Antigone Plantagenet, the legitimised daughter of Humphrey of Lancaster, 1st Duke of Gloucester (son of Henry IV and Mary de Bohun) and second wife Eleanor de Cobham.
Kynaston was the youngest son of Sir Roger Kynaston (c. 1432/1433–1495), High Sheriff of Shropshire, who is thought to have killed Lord Audley at the Battle of Blore Heath, and his second wife, Lady Elizabeth Grey, daughter of Henry Grey, 2nd Earl of Tankerville and Antigone Plantagenet, the legitimised daughter of Humphrey of Lancaster, 1st Duke of Gloucester (son of Henry IV and Mary de Bohun) and Eleanor de Cobham.