In 1488, Knollys was one of Henry VII's henchmen, and late in that year was appointed to wait on ‘the king's dearest son the prince’ (Arthur).
He received £5 ‘by way of reward’ for each of the three years 1488 to 1490, and when Henry VII met Archduke Philip in 1500, Knollys accompanied the English king as one of the ushers of the chamber.
He continued in the same office under Henry VIII, and received an annuity of £20, on 15 November 1509, and a grant of Upclatford, called Rookes Manor, in Hampshire — part of the confiscated property of Sir Richard Empson — on 10 February 1510/11.
On 9 July 1514, the usher and his wife were jointly granted the manor of Rotherfield Greys, near Henley-on-Thames, Oxfordshire, in survivorship, at an annual rental of a red rose at midsummer.
In 1562 he was sent on a diplomatic mission to Germany, to observe the temper of German Protestants, and in 1569 was temporarily employed in warding both Mary, Queen of Scots, at Tutbury and the Duke of Norfolk in the Tower.