Although various versions of the legend dispute her role in events, all invariably agree that she is the wife of Arthur and that she is unable to bear him a child. In Welsh tradition her reputation is not as bad as it later becomes, however several Welsh triads mention that the Battle of Camlann, in which Arthur and Mordred were allegedly killed, was the result of an argument between Guinevere and her sister. Welsh tradition presents Guinevere as beautiful, noble and yet tragic, and these characteristics are maintained in later versions of Arthurian legends. In English accounts she is increasingly portrayed as Arthur's treacherous and unfaithful wife. Her inability to give Arthur an heir makes her a failure as a queen and according to medieval values, also a failure as a woman. English chronicles tend to ignore the development of Guinevere's character. She is simply the woman who marries Arthur for political reasons and later betrays him by conspiring with Mordred to seize the throne. In later versions of the Arthurian story she is the lover of Lancelot and the cause of civil war between the Knights and the King, allowing Mordred to rebel against his king.

Nineteenth century English portrayals of Guinevere are particularly harsh due to the influence of strict Victorian morality. French Arthurian romances and modern interpretations attempt to explain Guinevere's infidelity, variously citing loneliness and frailty as the cause of her affair with Lancelot. There are conflicting versions of Guinevere's death. In some versions Guinevere dies during Arthur's reign. In others, she dies a prisoner of the Picts and French romances maintain that she died in a convent which she entered after Arthur's death. In some accounts of the legends there are implications that Arthur was married to three different women with names similar to Guinevere, and some argue that this shows that Guinevere is in fact a mythical figure representing sovereignty.