“The Tale of Sir Gareth” is the only one of Malory's tales that does not have a surviving major source, and, as the only one of Malory's eight that has no direct counterpart in any of the Old French cycles, it is Malory's most surprising addition to Arthur's biography. Of extant romances, it most closely resembles those of the Fair Unknown type, which include Renaut de Bâgé's French Le Bel Inconnu, the Middle English Lybeaus Desconus, Wirnt von Gravenburg's German Wigalois, the Italian Carduino, the French and English versions of Ipomedon, and the “Cote Mal Taile” episode of the Prose Tristan. It does not, however, resemble any of these romances closely enough for any of them to be taken as Malory's primary source.

“The Tale of Sir Gareth” story opens on a Pentecost, when Arthur, according to his custom, awaits a marvel or adventure before going to the feast. His custom is satisfied by the appearance of three men and a dwarf. One of the men, the yet unidentified Gareth, asks Arthur for three boons. The first is for a year's food and lodging, and he asks to be allowed to specify the final two at the end of the year. Arthur tells Gareth that food and lodging are available to all and that he should ask for something greater, but Gareth holds to his request. When asked, he will not reveal his name, and Kay therefore names him Beaumains, turning Gareth's fair hands into a cause for derision. Kay then puts him to work in the kitchens.