By the time James I ascended the throne, Knyvett, who should not be confused with his Norfolk namesakes, had spent more than 30 years in the royal Household, serving as keeper of both Westminster and Whitehall palaces. He rapidly emerged as a trusted servant of the Stuarts. In June 1605 he and his wife were appointed to care for the king’s short-lived infant daughter, Mary, at a fee of £20 a week.
As well as being keeper of two royal palaces, Knyvett was warden of the Mint, but his tenure of office was characterized by a long-running feud with his predecessor, the elderly Sir Richard Martyn, now master of the Mint. In 1601 Knyvett accused Martyn of not casting enough coins from the silver and copper alloy delivered to him,
In 1604 Knyvett was returned to Parliament for Westminster, the constituency which he had represented ever since 1584. Over the following four sessions he was named to 30 committees, many of which were concerned with purely local matters, such as the proliferation of new houses in the London area (24 Jan. 1606), the conversion of old buildings into smaller tenements (27 Apr. and 2 July 1604; 15 May 1607), the paving of Drury Lane (19 Mar. 1606) and the clarification of a Henrician statute regarding Southwark churchwardens (25 Feb. 1607).
By the time he was elevated to the peerage, Knyvett was in his early sixties. He subsequently decided to share the wardenship of the Mint with his protégé, Edmund Doubleday*, and to surrender the keeperships of Westminster and Whitehall palaces. Childless, he drew up his will on 20 July 1620, in which he declared that he believed ‘every article of the Nicene, Athanasian and Apostolic Creed literally, without ambiguity or doubt’. He also left £40 for the relief of the poor of Staines and Stanwell, and in a codicil dated 17 July 1622, instructed his wife and executrix to build a free school and schoolmaster’s residence in Stanwell within two years of his death.
