After practicing at Florence and Rome in Italy, he was invited by Francis I of France to come to Paris to be a personal doctor and teach at the Collège de France. While in Paris, Guido Guidi befriended artist Benvenuto Cellini and published a book on surgery, Chirugia, in 1544. This book was one of the best illustrated at the time and was based on works of Hippocrates, Galen, and Oribasius.
In 1557, Guidi returned to Italy to become the personal physician of Cosimo di Medici and taught at Pisa. He took holy orders and was ennobled. A book on medicine, incomplete at his death in 1569, was finished by his nephew as Ars Medicinalis between 1596 and 1611.