Second son of Lord Tytos Lannister and Lady Jeyne Marbrand, born at Casterly Rock and bound to his elder brother Tywin from the cradle. Sent young to Castamere to page and squire for Lord Roger Reyne, he was knighted by Lord Reyne in the War of the Ninepenny Kings, and thereafter served Tywin without complaint, content to live in the shadow of a brother whose competency he recognized early. When Tywin set about scouring the westerlands of robber knights and calling in the debts owed Casterly Rock, it was Kevan who rode out to do the work; Ser Harys Swyft, unable to pay, surrendered his daughter Dorna into Kevan's keeping, and Kevan in time fell in love with her and wed her by 266 AC. From her he had four children: Lancel, the twins Willem and Martyn, and the little maid Janei.
A household knight without lands of his own, Kevan kept two hundred knights at his command and chests of coin set by from Tywin's rewards and his father's bequest, and he shared every counsel his brother kept. He rode with Tywin into the riverlands at the outbreak of the War of the Five Kings, and at the battle on the Green Fork commanded the great mixed center while Tywin meant the left to break and Kevan to wheel the host against the Green Fork; cautious Lord Roose Bolton withdrew rather than walk into the snare. Willem was taken with Jaime in the Whispering Wood, Martyn fell to Robb Stark at Oxcross, and Kevan thereafter loosed Ser Gregor Clegane, Ser Amory Lorch, and Vargo Hoat upon the riverlands at Tywin's order. King Joffrey set him on the small council as master of laws, and after the Red Wedding he stood at Tywin's side until Tyrion put a quarrel through their father in the Tower of the Hand.
When Cersei offered him the Handship, Kevan refused unless she would name him regent for King Tommen and return herself to Casterly Rock as Lady, urging her instead to bestow the white wand upon Lord Mathis Rowan or Lord Randyll Tarly; she threw wine in his face and he carried Tywin's body west with a hundred crossbows and three hundred men-at-arms behind him. Only when the Faith took Cersei did he accept the regency from Grand Maester Pycelle and Ser Harys, and he came back to King's Landing styled Lord Regent and Protector of the Realm to mend what his niece had broken. He named Lord Mace Tyrell Hand of the King, Lord Paxter Redwyne master of ships, and Lord Randyll Tarly master of laws, sent his good-father Harys to treat with the Iron Bank at Braavos, and weighed the threat of Jon Connington and the boy called Aegon at the head of the Golden Company. Summoned after supper to Pycelle's chamber, he found the Grand Maester slain beneath a white raven that proclaimed the coming of winter; Varys stepped from the shadows with a crossbow, said he bore Kevan no malice but could not suffer him to undo Cersei's misrule, and bade his little birds finish what the quarrel had begun.