While serving as abbess, d'Harcourt wrote Life of Isabella, the biography of her friend, colleague, and eventual saint, Isabelle.
[2] d'Harcourt was the first Longchamp abbess to be re-elected to the position after an interim period of other leadership, indicating that the sisters in residence felt confident in her abilities.
Through her role as abbess, d'Harcourt was responsible for buying land, negotiating for rents, and securing royal confirmation of the abbey’s purchases; records also indicate her involvement in filing a legal claim regarding the enforcement of a will.
Analysis of the surviving records reveals a female leader who was “more literate, more adept at dealing with written documents, and more forceful in legal matters than her contemporaries.”[2] Two examples of d'Harcourt’s writing survive: Letter on Louis IX and Longchamp and The Life of Our Holy and Blessed Lady and Mother Madame Isabelle of France, known later as The Life of Isabelle of France (the production of which may make Agnes d'Harcourt “the first woman to have written an extant work of French prose”).
Her methods, according to Allirot, indicate “a strong awareness of the historical importance of written evidence.”[4] d'Harcourt is a featured figure on Judy Chicago's installation piece The Dinner Party, being represented as one of the 999 names on the Heritage Floor.