Born in Northumberland, Balin somehow slew a cousin of Arthur's, for which Arthur imprisoned him for half a year. Balin was out of prison, but impoverished and still remaining at Arthur's court, when a damsel to whom I have arbitrarily assigned the name "Malvis" came to Camelot girded with the sword referred to as Balin's Sword. When Balin, alone of the knights at court, had drawn the sword, the first English Lady of the Lake (not Nimue, but the one I call "Nineve") came to Arthur to demand either Balin's head or that of "Malvis" in return for Excalibur. The Lady of the Lake claimed that Balin had slain her brother. As Arthur tried to put her off, Balin saw her, heard she was asking for his head, and lopped off hers instead, explaining that she had caused his mother to be burnt. Arthur, annoyed, dismissed Balin from the court. Sir Lanceor of Ireland rode out after Balin, challenged him, and died of Balin's spear when they jousted; Lanceor's lady Colombe, finding him dead, slew herself before Balin could stop her. Balin's brother Balan found him here, and shortly thereafter King Mark happened by. When Mark asked their names, Balan told him, "Sir ... ye may see he beareth two swords, thereby ye may call him the Knight with the Two Swords."

Balin and Balan next got back Arthur's favor by capturing his enemy King Ryons in ambush and then joining the battle before Castle Terrabil on Arthur's side. Lamorak de Galis was to claim, years later, that Balin had been the one who had killed King Lot in that battle.

"Oh, where is Balin and Balan and Pellinore? said King Arthur [after the battle]. As for Pellinore, said Merlin, he will meet you soon; and as for Balin he will not be long from you; but the other brother will depart, ye shall see him no more. By my faith, said Arthur, they are two marvellous knights, and namely Balin passeth of prewess of any knight that ever I found, for much beholden am I unto him; would God he would abide with me."

[Lancelot had not yet come to Britain, and Gawaine was still young and scarcely tried.]

Balin did return to Arthur, but only very briefly. Seeing Sir Herlews le Berbeus and his lady ride by his pavilion toward the castle of Meliot, Arthur sent Balin after them, and on the way back Herlews was slain by Sir Garlon, who rode invisible. Balin thereupon rode with Sir Herlew's lady in pursuit of Garlon, whom they traced by his other murders and depredations. They stopped one night at the castle of the Leprous Lady. Eventually tracking Garlon to King Pellam's castle, Balin succeeded in exterminating the villainous knight. He and the lady lingered, however, to collect some of Garlon's blood in order to heal a youth Garlon had left wounded. This gave Garlon's brother Pellam time to call for his weapon and go after Balin. Balin's sword breaking at the first stroke, he fled from Pellam until he found Longinus' Spear and dealt Pellam the Dolorous Stroke. The castle collapsed about them, killing Sir Herlew's lady. In three days Merlin released Balin from the wreckage.

After one or two other adventures, Balin came to the castle described under 'Meliot'. Here, to fulfill the customs of the place, Balin fought his brother Balan; Balan (having conquered the previous defender of the island) wore that knight's red armor, while Balin borrowed a shield offered to him for the occasion by one of the castle's knights. Thus neither recognized the other until after both were mortally wounded. Merlin later refurbished Balin's sword for Galahad. (The sword that Pellam had broken may have been the one Balin had, even before he drew that of "Malvis"; he wore only one of his two swords into the hall where he found and slew Garlon.)

Although apparently never a companion of the Round Table, and seemingly doomed to do unfortunate deeds, Balin seems to have been a very sincere and well meaning knight as well as a capable and valorous one.