She devoted the rest of her life to writing, both nonfiction and well-researched fiction. She never attended university but became a self-taught scholar in areas that interested her, especially Shropshire and Wales. Birmingham University gave her an honorary master's degree. She never married, but did fall in love with a Czech man. She remained friends with him after he married another woman.[7] She was pleased that she could support herself with her writing from the time after the Second World War until her death.[7]
Pargeter wrote under a number of pseudonyms; it was under the name Ellis Peters that she wrote her later crime stories, especially the highly popular series of Brother Cadfael medieval mysteries, featuring a Benedictine monk at the Abbey in Shrewsbury. That pseudonym was drawn from the name of her brother, Ellis, and a version of the name of the daughter of friends, Petra.[7] Many of the novels were made into films for television. Although she won her first award for a novel written in 1963, her greatest fame and sales came with the Cadfael Chronicles, which began in 1977. At the time that the 19th novel was published, sales of the series exceeded 6.5 million.[7] The Cadfael Chronicles drew international attention to Shrewsbury and its history, and greatly increased tourism to the town. In an interview in 1993, she mentioned her own work before the Second World War as a chemist's assistant, where they prepared many of the compounds they sold. "We used to make bottled medicine that we compounded specially, with ingredients like gentian, rosemary, horehound. You never see that nowadays; those tinctures are never prescribed. They often had bitters of some sort in them, a taste I rather liked. Some of Cadfael's prescriptions come out of those years."[8]
Her Cadfael novels show great appreciation for the ideals of medieval Catholic Christianity, but also a recognition of its weaknesses, such as quarrels over the finer points of theology (The Heretic's Apprentice), and the desire of the church to own more and more land and wealth (Monk's Hood, Saint Peter's Fair, The Rose Rent).
