So what do we know about her life? She was born in Norfolk, in England around 1373. She married John Kempe sometime before 1394 and the couple had several children, at least one of whom survived to adulthood. The pair separated sometime around 1420, though she did return to nurse him when he fell ill a little less than a decade later.
Throughout her life, she developed a strong sense of religious devotion. There is no evidence as to whether or not she ever learned to read,** though as an adult she had a priest read religious works to her. She eventually ended up memorizing scripture rather than be dependent on anyone else for access to it. When the time came to write about her experiences, she dictated them to a priest. She was also very public about her devotion, carrying out public displays of prayer and penance and making no secret of the fact that she had visions.
For a while she ran both a brewery and a grain mill out of her home, but when these failed she decided to focus her attention on her religion. She spent much of her time on pilgrimage and visited many of the important religious figures and sites in England at the time. She traveled widely, both on her own and with her daughter-in-law. She was arrested multiple times, usually on accusations of heresy (Lollardy, to be specific), but she was released each time and eventually returned home.
Her Book focuses primarily, though not only, on the religious aspect of her life. It tells us a lot, not only about her as a person, but also about middle class women in England at this time. She traveled widely. She ran her own businesses, however short-lived they might have been. She used her religious experiences to her own benefit and eventually translated these into a written work that survives today.
*Depending on one’s definition of “secular autobiography,” one could also call it one of the few secular autobiographies between Late Antiquity and the Renaissance. If one defines the term as a work written by a member of the laity, then Margery Kempe’s work definitely counts. If, however, one defines it as a work that is not in large part about the author’s religious experiences, then it does not count. The work of Benvenuto Cellini is usually given the honor of being called the first. To be honest, it seems in some ways a rather arbitrary distinction. I’m not saying that thinking about it isn’t important, just that it’s arbitrary.
**The Wikipedia article brings this up repeatedly and uses it to show that she was illiterate. This is not how evidence works. It is probable that she could neither read nor write. This is still not how evidence works.