The Mirror of Simple Annihilated Souls and Those Who Only Remain in Will and Desire of Love is regarded as one of the most enigmatic and influential manuscripts in the history of medieval Christian mysticism. Its author was not known until the mid-twentieth century. In 1946, Romana Guarnieri identified Marguerite Porete, condemned and burned at the stake for “relapsed heresy” in Paris in 1310, as the author of this book. This paper aims to introduce Marguerite Porete, who is one of the most interesting forgotten women thinkers in the history of ideas. It will present the major sequences of her life, recount the rediscovery of The Mirror of Simple Souls by Guarnieri, and focus on its literary structure and certain philosophical themes it contains or implies. These selected themes are as follows: the subversion of the distinction between the learned and the ignorant, the opposition between Reason and Love, a naturalism beyond ascetism, a call for the constitution of a new subjectivity “beyond good and evil” and a concept of annihilation that denies the existence of free will.