Margaret of Antioch appears first in sources from the 9th century onward, with no mention in any patristic or early medieval source. The earliest reference is in a Byzantine list of martyrs compiled centuries after the alleged date of her martyrdom. The Acta Sanctae Margaretae (Acts of Saint Margaret), the primary narrative source, is a medieval composition with no claim to documentary foundation or eyewitness authority.

According to the Acta, Margaret was the daughter of a pagan priest at Antioch. She converted to Christianity and took vows of virginity. When a pagan official became enamored of her and sought to force her to marry him, she refused. Under interrogation and torture, she remained steadfast in her faith and was eventually executed. The Acta adds that during her ordeal in prison, she encountered a dragon (or demon) that attempted to devour her, but she made the sign of the cross, and the creature burst asunder.

No patristic source mentions Margaret. She does not appear in Eusebius's Ecclesiastical History, which details the persecutions of her alleged era. She is absent from Jerome's De Viris Illustribus and from the Depositio Martyrum. The silence of all early sources is significant and suggests she may not be a historical figure at all, but rather a legendary saint whose cult arose in the medieval period.

Traditionally, Margaret is portrayed as a beautiful young virgin of high birth, devoted to Christianity. She resisted marriage proposals and refused to abandon her faith despite torture and threats. According to the most famous legend, a demon or dragon attempted to devour her, but she made the sign of the cross, and the creature split open, releasing her unharmed. She is typically shown standing on or over a dragon, often with a cross in hand. Medieval art frequently depicts her as a graceful figure in elegant dress, sometimes holding a chain attached to the dragon.