Although Malory continues to follow the story as given in the Vulgate Cycle, as a narrative unit, “The Tale of Sir Launcelot and Queen Guinevere” is Malory's invention. It consists of narrative threads from the first half of two major sources and a single episode from a third. The first two sources are La mort Artu, the last romance of the Vulgate Cycle, and the English stanzaic Le Morte Arthur, which is itself based on the Vulgate Mort Artu and tells much the same story. The third major source is probably part of the Vulgate Lancelot but could also have been Chrétien de Troyes's Le chevalier de la charrete, which is the source for that episode in the Vulgate Cycle. Malory's treatment of the sources of this tale is similar to his treatment of the sources of “The Tale of Sir Launcelot.” In both tales, Malory takes episodes from his sources, creates linking material, and includes an episode for which no source is known.

The narrative structure of this tale is built around the increasing tension of conflict and resolution in the love affair of Lancelot and Guinevere. In the aftermath of the Grail quest, Lancelot returns with renewed heat to his love of Guinevere, which he had repressed during the quest. When scandal threatens, however, he begins to avoid the queen. This leads to a quarrel, in which she banishes him from the court.