Malory's sixth tale is a close adaptation of the Vulgate Queste del Saint Graal. At Pentecost, 454 years after the Passion, Galahad arrives at Arthur's court. He achieves the adventures of the sword in the stone and of the Siege Perilous, adventures which no knight previously could achieve. The Grail appears in Arthur's court covered in white samite, feeds each person the food that he likes best, and vanishes. The knights of the Round Table, led by Gawain, vow to search until they can see the Grail openly. On the quest, each knight's spiritual worthiness is revealed by the adventures that he encounters. Nearly all of the knights are killed or else return to court without gaining a glimpse of the Grail. Lancelot, trying to repent his adulterous relationship with Guinevere, receives a partial vision of the Grail, but of Arthur's knights only Galahad, Perceval, and Bors see the Grail fully. After Galahad heals the wound of the Maimed King, these three knights take the Grail to the city of Sarras in the Holy Land, where Galahad becomes king. After a short time, Galahad requests and receives his bodily death. The Grail is borne up to Heaven. Perceval dies shortly thereafter, and Bors returns to Camelot.

Malory follows the major source of this tale with greater fidelity than that of any other of the eight tales. He follows the French Queste from its beginning to its ending without omitting or altering any of its key events. The most notable change that he makes in his material is abbreviation of the exegesis of the knights’ adventures given by various hermits. In addition to including a greater percentage of his major source than in other tales, Malory adds far fewer elements from minor sources than in any other.