Some time after 1571, he left Oxford to become headmaster at a grammar school in Sandwich, Kent, which was founded by Sir Roger Manwood in about 1563.
[2] After Manwood's death in 1592, his son, Sir Peter became Knolles' professional and literary patron and encouraged him to write.
Knolles also published a composite translation of Jean Bodin's Les Six livres de la République in 1606, under the title The Six Bookes of a Commonweale.
Samuel Johnson praised him as the best of English historians, saying that "in his history of the Turks [Knolles] has displayed all the excellencies that narration can admit."
Johnson explained Knolles' limited reputation by pointing out that his history recounted "enterprizes and revolutions, of which none desire to be informed".