Henry was born at London, Middlesex on April 3, 1559 and was seven months of age at his father's death. He married Magdalen c1580. His name was also spelt, Knevett, Knevet and Knevit.

Elizabeth I gave the wardship of Henry Knevet at age 3, for upbringing and for conformity, to Sir William More her most trusted agent and sheriff in Surrey who helped to eliminate the Catholic presence south of London late in her reign. Sir William had just completed his new manor house at Losely just south of Guilford in 1569 when Elizabeth visited, accompanied by the 4th Duke of Norfolk, Thomas Howard. Norfolk was in clandestine correspondence by code with Mary Queen of Scots, held in the vicinity of Sheffield castle, promising marriage without sanction from the queen of England, and there was possible higher status for the Duke. The Duke a romantic; starved by lack or opportunity in Elizabeth's government did not take this opportunity to explain himself to the Queen, but he met the children at Losely and apparently bought the wardship of Henry Knevit then at the age of eleven.

Henry Knevit next appears listed in the ciphers found at the Norfolk House (Charterhouse) in 1572 at the time of the Duke's trial and execution. He was apparently a messenger for Norfolk for two years. He entered Magdalen College at Oxford in 1571 at the actual age of 13, a somewhat common occurrence at the time. The alumni records or Oxford and Cambridge confuse Henry Knevit of the Radford Semele manor of Warwickshire with Henry Knyvet of Ashwellthrop, Norfolk.

Henry was sent to the continent by Walsingham, the vigilant conformer, as a carrier and cipher expert in l577-78.

In 1589 Henry Knevet sold Radford Semele to John Browne Of Barnham, Sussex.