Joseph first appears in the four Gospels of the New Testament as a member of the Sanhedrin, the Jewish council that had condemned Jesus to death. Matthew calls him a rich man and a disciple of Jesus. After the crucifixion, when the other disciples had fled in fear, Joseph went boldly to Pontius Pilate and asked for the body of Christ. He wrapped it in a clean linen cloth and laid it in his own new tomb, hewn from rock in a garden. But the Arthurian legends go far beyond the biblical account. In the late 12th-century verse romance Joseph d'Arimathie by Robert de Boron, a Burgundian knight-poet, Joseph was present at the Last Supper and kept the cup from which Christ had drunk. After the crucifixion, he used that same cup to catch the blood that flowed from the wounds of the Saviour, and the vessel was transformed into the Holy Grail, twice-hallowed by the body and blood of Christ.

Robert de Boron tells how Joseph was imprisoned by the Jews for his devotion to Christ. For forty years he languished in a dungeon, sustained only by the Grail, which appeared to him daily with the divine food that kept him alive. When he was finally released, Jesus appeared to him in a vision and commanded him to gather a fellowship of followers. Joseph created the Grail Table, a sacred board with twelve places in memory of the twelve apostles, with one seat left empty for the Messiah who would one day return. But the fellowship was not without sin. When they held a banquet, those who were righteous were filled with sweetness from the Grail, while the sinners went hungry. Joseph's brother-in-law, Bron, also called Hebron, was declared the Rich Fisherman because he alone caught a fish that fed the whole company. Joseph entrusted the Grail to Bron and his wife Enygeus, and the fellowship set out for the west, carrying the sacred vessel to the Vales of Avalon, the mysterious realm that would one day be identified with Glastonbury in Somerset.

The Vulgate Cycle, the vast prose romance composed in the early 13th century, expanded Joseph's story into the Estoire del Saint Graal, the History of the Holy Grail. In this version, Joseph and his son Josephe, who had been miraculously consecrated as the first bishop of Britain by Christ himself, travelled with the Grail and converted several pagan kings. They came to the city of Sarras, where King Evelake had been promised that he would see the sacred vessel before he died. Joseph and Josephe baptised Evelake and his people, and the king built a shrine to house the Grail. Josephe later travelled to Britain and established the Grail community there, while Joseph's spirit remained present at the climactic Mass of the Grail, celebrated centuries later when Galahad, Percival, and Bors achieved the final vision of the vessel. The Vulgate also introduced the bleeding lance, the spear of Longinus that had pierced Christ's side, as a companion relic to the Grail, both brought to Britain by Joseph's fellowship.

The connection between Joseph and Glastonbury Abbey became one of the most enduring legends in British history. In the 14th century, the monk John of Glastonbury wrote a chronicle claiming that Joseph had been sent to Britain by Saint Philip the Apostle after preaching in Gaul. He brought with him two cruets, vessels containing the blood and sweat of Christ, and he founded the first Christian church in Britain on the site of what would become Glastonbury Abbey. The most famous story tells how Joseph climbed Wearyall Hill, exhausted from his journey, and thrust his pilgrim staff into the ground. By morning the staff had taken root and blossomed into a hawthorn tree, the Glastonbury Thorn, which flowers at Christmas and Easter to this day. John of Glastonbury even claimed that King Arthur was descended from Joseph through his mother, Igraine, giving the legendary king a sacred lineage that connected him to the Holy Land itself.

In Robert de Boron's sequel, the romance Merlin, the wizard revealed that the Round Table of King Arthur was modelled upon Joseph's Grail Table. Uther Pendragon had established the Round Table with twelve seats for the greatest knights, with one place left empty, just as Joseph had left a place for Christ. This connection made the Grail quest the spiritual destiny of Arthur's fellowship, for the knights who sought the Grail were seeking the relic that their founder's ancestor had brought to Britain. The lineage of Grail guardians passed from Joseph to Josephe, then to Bron the Rich Fisherman, then to Alain le Gros, and through generations of Fisher Kings until it reached King Pelles of Corbenic, the wounded keeper of the Grail Castle, and ultimately to his grandson Galahad, the perfect knight who achieved the vessel that Joseph had carried from Jerusalem. Joseph of Arimathea thus stands at the origin of everything that makes Arthurian legend sacred, the man who turned a cup and a tomb into the foundations of a myth that has lasted a thousand years.