He married Catherine Carey, first cousin (as well as possible half-sister) of Queen Elizabeth I. Henry VIII extended to him the favour that he had shown to his father, and secured to him in fee the estate of Rotherfield Greys in 1538.

[2] At the beginning of Edward VI's reign, he accompanied the English army to Scotland, and was knighted by the commander-in-chief, the Duke of Somerset, at the camp at Roxburgh on 28 September 1547.

[2] Knollys' strong Protestant convictions recommended him to the young king, and to his sister the Princess Elizabeth, and he spent much time at court, taking a prominent part not only in tournaments there, but also in religious discussion.

[2] Before Mary's death he returned to England, and as a man "of assured understanding and truth, and well affected to the Protestant religion," he was admitted to Elizabeth's privy council in December 1558.

[4] Throughout his parliamentary career he was a frequent spokesman for the government on questions of general politics, but in ecclesiastical matters he preserved as a zealous puritan an independent attitude.

In 1563 he was governor of Portsmouth, and was much harassed in August by the difficulties of supplying the needs in men and money of the Earl of Warwick, who was engaged on his disastrous expedition to Le Havre.

[5][6] On 13 July Knollys contrived to remove her, despite "'her tragical demonstrations", to Bolton Castle, the seat of Lord Scrope, where he tried to amuse her by teaching her to write and speak English.

[7] Knollys's position grew more and more distasteful, and writing on 16 July to Cecil, whom he kept well informed of Mary's conversation and conduct, he angrily demanded his recall.

But while lamenting his occupation, Knollys conscientiously endeavoured to convert his prisoner to his puritanic views, and she read the English prayer-book under his guidance.

[9] In October, when schemes for marrying Mary to an English nobleman were under consideration, Knollys proposed that his wife's nephew, George Carey, might prove a suitable match.

In November the inquiry into Mary's misdeeds which had begun at York, was reopened at Westminster, and Knollys pointed out that he needed a larger company of retainers to keep his prisoner safe from a possible attempt at rescue.

[2] In April 1571 Knollys strongly supported the retrospective clauses of the bill for the better protection of Queen Elizabeth, by which any person who had previously put forward a claim to the throne was adjudged guilty of high treason.

Her unwillingness to take "safe counsel", her apparent readiness to encourage parasites and flatterers, whom he called "King Richard the Second's men", was, he boldly pointed out, responsible for most of her dangers and difficulties.

In July 1578 he repeated his warnings in a long letter, and begged her to adopt straightforward measures so as to avert such disasters as the conquest of the Low Countries by Spain, the revolt of Scotland to France and Mary Stuart, and the growth of papists in England.

He did not oppose the first proposals for the queen's marriage with Alençon which were made in 1579, but during the negotiations he showed reluctance to accept the scheme, and Elizabeth threatened that "his zeal for religion would cost him dear".

But he was zealous in opposition to heresy, and in September 1581 he begged Burghley and Robert Dudley, 1st Earl of Leicester to repress such "anabaptisticall sectaries" as members of the "Family of Love", "who do serve the turn of the papists".

This speech, "related by himself" to Burghley, was published in 1608, together with a letter to Knollys from his friend, the puritan John Rainolds, in which Bishop Bancroft's sermon at St Paul's Cross (9 February 1588–9) was keenly criticised.

Knollys' contribution reappeared as "Speeches used in the parliament by Sir Francis Knoles", in William Stoughton's "Assertion for True and Christian Church Policie" (London, 1642).

The wayward temper of his grandson, Robert Devereux, 2nd Earl of Essex (son of his daughter Lettice by her first husband), was a source of trouble to him in his later years, and the queen seemed inclined to make him responsible for the youth's vagaries.