The legend of the fourth century Saint Mary Egyptiaca was already current in a written form as early as the sixth century; it was elaborated during the following centuries and is related in detail by Jacopo da Varagine in the Leggenda Aurea. Saint Mary became a prostitute in Alexandria at the age of twelve and was converted to Christianity in Jerusalem seventeen years later. Renouncing her former life, she retired in penance to the desert beyond the Jordan, remaining there undisturbed until she was discovered forty-seven years later by a priest named Zosimus. She requested him to tell nobody and to return a year later with the Holy Sacrament. This he did, and she tearfully confessed and took communion. On his third visit, Zosimus found her dead with a message written in the sand asking him to bury her. Although the worship of Saint Mary of Egypt was fairly widespread in Italy and France, images of her are relatively rare, especially in comparison with those of her namesake the Magdalen, whose story forms so close a parallel.

According to the catalogue of the 1961 exhibition, Dr. Mario d'Orsi dated the present picture to Giaquinto's years in Spain, 1753-1762, comparing it to the Penitent Magdalen in Caracas (M. d'Orsi, Corrado Giaquinto, Rome, 1958, fig. 148). It is a rare example of a signed painting by the artist, the signature indicating that it was intended as a finished picture rather than a modello for a larger work. An unsigned version is in the collection of Francesco Molinari Pradelli, Marano di Castenaso, near Bologna (Dania, op. cit., p. 823, fig. 813; Catalano, loc. cit., no. 44, illustrated in colour)