Porete's life is recorded only in accounts of her trial for heresy, at which she was condemned to be burnt at the stake. Her biography is probably biased and certainly incomplete. She is associated with the Beguine movement, and was therefore able to travel fairly freely. Some also associated her with the Brethren of the Free Spirit movement, a group which was considered heretical because of their antinomian views. The connection between Porete and the Free Spirits is somewhat tenuous, though, as further scholarship has determined that they were less closely related than some Church authorities believed.

Unlike other religious figures such as Meister Eckhart, who were condemned and later rehabilitated by the Roman Catholic Church, it is unlikely that Porete will be so favored. This is partly due to her relative obscurity. Until 1946, it was not even known that she was the writer of the Mirror, which had been published anonymously since her death.

The title of Porete's book refers to the simple soul which is united with God and has no will other than His. The book was originally written in Old French, but was translated into Latin and other languages and circulated widely. Some of the language, as well as the format of a dialogue between characters such as Love, Virtue and the Soul, reflects a familiarity with the style of courtly love which was popular at the time, and attests to Porete's high level of education and sophistication.

Although much of her book resembles a rational, Boethian argument between several parties it is actually subverting those expectations. Writing in beautifully elegant, flowing poetic prose and occasionally poetry, Marguerite ultimately says that the Soul must give up Reason, whose logical, conventional grasp of reality cannot fully comprehend God and the presence of Divine Love. The "Annihilated Soul" is one that has given up everything but God through Love. For Porete, when the Soul is truly full of God's Love it is united with God and thus in a state of union which causes it to transcend the contradictions of this world. In such a beatific state it cannot sin because it is wholly united with God's Will and thus incapable of acting in such a way - a phenomenon which the standard theology describes as the effect of Divine grace, which suppresses a person's sinful nature. It is in this vision of Man being united with God through Love, thus returning to its source, and the presence of God in everything that she connects in thought with the ideas of Eckhart. Porete and Eckhart had acquaintances in common and there is much speculation as to whether they ever met or had access to each other's work.

In many ways Porete's vision is the highest expression of the words of John the Evangelist in the New Testament:

"Beloved, let us love one another, for love cometh of God. And every one that loveth, is born of God, and knoweth God. He that loveth not, knoweth not God; for God is love. .. [and] he that dwelleth in love dwelleth in God, and God in him." (First Epistle of John 3: 7-16)

Words which Porete herself references in her own writing:

" I am God, says Love, for Love is God and God is Love, and this Soul is God by the condition of Love. I am God by divine nature and this Soul is God by the condition of Love. Thus this precious beloved of mine is taught and guided by me, without herself, for she is transformed into me, and such a perfect one, says Love, takes my nourishment." (The Mirror Of Simple Souls. Trans. Ellen Babinsky ISBN 0809134276)

Porete's vision of the Soul in ecstatic union with God, moving in a state of perpetual joy and peace, is a repetition of the Catholic doctrine of the Beatific Vision, albeit experienced in this life and not in the next. Where Porete ran into trouble with some authorities was in her description of the Soul in this state being above the worldy dialectic of conventional morality and the teachings and control of the earthly church. Porete argues that the Soul in such a sublime state is above the demands of ordinary virtue, not because virtue is not needed but because in its state of union with God virtue becomes automatic. As God can do no evil and cannot sin, the exalted/Annihilated soul, in perfect union with Him, no longer is capable of evil or sin. Although this concept is found in the catechism, certain Church authorities nevertheless claimed that it smacked of amorality.

Interestingly, two hundred years later St John of the Cross expressed an almost identical view of the nature of the Soul's union with God in his The Ascent Of Mount Carmel i.e. that once united with God the Soul's will becomes that of God's, but was not denounced as a heretic. Although the Mirror is now embraced as an important piece of Christian mysticism it is unlikely Porete will ever enjoy the renown or acceptance John now receives from the Catholic Church.

Porete had been officially warned by Church authorities that her work was heretical and had her books publicly burned by the Bishop of Cambrai at Valenciennes. One of the taboos Porete had broken was writing the book in Old French rather than in Latin and she was ordered not to circulate her ideas or the book again. Nevertheless she continued to do so and was eventually arrested by the local Inquisitor on grounds of heresy, in spite of claims in the book that she had consulted three church authorities about her writings, including the highly respected Master of Theology Godfrey of Fontaines, and gained their approval.

Medieval manuals on "discretio spirituum" ... the clerical judgement of mystical visions ... called for the clergy to serve in an advisory role but nevertheless cautioned them about their own ultimate inability to make a definitive judgement on such matters (see late-medieval manuals such as Gerson's "De probatione spirituum" and "De distinctione verarum visionum a falsis"). Such manuals tell the clergy to provide learned guidance, not ultimate judgement, warning them that they might make a mistake and end up opposing the Divine Will. Seemingly ignoring such calls for caution, William of Paris consulted with a total of twenty-one theologians who scoured The Mirror of Simple Souls for evidence of heresy. Among those who condemned the book were the ecclesiastical textual scholar, Nicholas of Lyra.Three Bishops passed final judgement upon her.

Porete had been arrested with a Beghard, Guiard de Cressonessart, who was also put on trial for heresy. Guiard declared himself to be Porete's defender. After being held in prison in Paris for a year and a half, their trial began. Guiard, under tremendous pressure, eventually confessed and was found guilty. Porete, on the other hand, refused to recant her ideas, withdraw her book or cooperate with the authorities, refusing to take the oath required by the Inquisitor to proceed with the trial. Guiard, because he confessed, was imprisoned. Porete, because she did not, was found guilty and burnt at the stake as a relapsed heretic. The Inquisitor spoke of her as a 'pseudo-mulier' ('fake woman') and described the Mirror as 'filled with errors and heresies'. As she died, the crowd was moved to tears by the calmness of how she faced her end. A record of the trial was appended to the chronicle begun by William of Nangis.

After her death extracts from the book were used at the Council of Vienne in 1312 to condemn the Free Spirit movement as heretical.

There is much speculation as to why Porete became such a target and why so much effort was made to put her on trial (the amount of consultants gathered to draw up the case against her was unprecedented). Growing hostility to the Beguine movement among Franciscans and Dominicans, the political machinations of the French king Philip the Fair, who was also busy suppressing the Knights Templar, ecclesiastical fear at the spread of the anti-hierarchical Free Spirit Heresy have all been suggested, as has the popularity of Porete's book which gave her a profile other writers did not have. Even after her death the Mirror of Simple Souls continued to be distributed across Europe, where it was translated into several languages, including English. In spite of its reputation as a heretical work it remained popular in Medieval times and in some ecclesiastical centres was embraced as an almost canonical piece of theology. Between Porete's death and the identification of her as the work's author in the last century, however, the Mirror was circulated as an anonymous work, Porete's name having been struck from it. Curiously, as an anonymous work it caused less controversy and in some instances was embraced as an acceptable part of Christian literature and thought (at one point it was thought that John of Ruysbroek had written it). This perhaps says something interesting about the complexities surrounding the nature of the book and the way it was received in its day. It is possible that Porete's femininity or the timing of the Mirror's publication at the height of the Free Spirit controversy lent weight to its persecution.

There were numerous female mystics during the Middle Ages period who all (by definition) claimed direct mystical contact with God, some working from within the framework of the Church, some not; and yet most ... such as Hildegard of Bingen, Catherine of Siena, Birgitta of Sweden, Julian of Norwich, etc. ... were not viewed as suspect. Nevertheless the leader of her trial, the Dominican Inquisitor William of Paris gathered together a formidable array of academics and lawyers to assess the case against Porete.

Since the publication of the original Old French version of the Mirror of Simple Souls in 1965 Porete's status as one of the greatest of Medieval Mystics has grown, placing her alongside Mechthild of Magdeburg and Hadewijch as one of the most visionary exponents of the Love Mysticism of Beguine spirituality.

In 2006 poet Anne Carson wrote a poetic libretto entitled Decreation, the second part of which takes as its subject Marguerite Porete and her work, the Mirror of Simple Souls as part of exploration of how women (Sappho, Simone Weil and Porete) "tell God".