Bruno became an itinerant teacher in several places in Italy, including Noli, Turin, Venice and Padua. But soon he quit the country all together.
In 1582, while Bruno was living Paris, he wrote his first literary work, Il Candelaio, a comedy. While in England he met the poets Sir Philip Sidney and Sir Fulke-Greville, debated at Oxford and wrote several philosophical dialogues, including Ash Wednesday Supper (1584). He also defended the Copernican system and his own notion of the infinite universe. In 1584 two of his books were published, On Cause, Principle, and Unity and On the Infinite Universe and Its Worlds.
This latter book is probably the one that caused him the most trouble, as he suggested there were other worlds with life on them besides the Earth. His books also rejected Aristotelian metaphysics, which posited that the Universe was fixed and finite. His Banishment of the Triumphant Beast was dedicated to Sir Philip Sidney and is a treatise on ethics and Cabala of the Pegasean Steed is a satire about ignorance, written in the form of an ironic praise of stupidity. De gli heroici furori (1585) is also dedicated to Sidney and deals with heroic enthusiasms like the aspirations of the intellect and the inspirations of poetry. The work features a group of poems written by Bruno and the Petrarchean poet Luigi Tansillo.
While in Paris, Bruno cultivated powerful patrons, including Henry III, who was so impressed with Bruno’s studies in mnemonics that he gave him a lectureship and put him on salary. During this time Bruno wrote a few books on mnemonics, including Ars Memoriae.