Ser Kevan is a loyal adviser to his older brother Lord Tywin Lannister and one of the topmost officers in the Lannister armies during the War of the Five Kings. After the arrest of his niece, Queen Mother Cersei Lannister, Grand Maester Pycelle offers Kevan the position of Hand of the King, which he accepts and, shortly thereafter, he returns to King's Landing.
Kevan is the second son of the late Lord Tytos Lannister. He is the brother of Lord Tywin Lannister the head of House Lannister and Lord of Casterly Rock. Kevan is married to Dorna Lannister and they have a son Lancel, who is a squire to King Robert Baratheon. He is a noted knight who served his elder brother loyally as an adviser, and is respected for his wise and candid counsel.
While talking with his mother on how to handle the North should it come to conflict with the Starks, Prince Joffrey muses on crushing the Northerners with a new "Royal Army" and giving Winterfell to his great-uncle Kevan to rule over. Though, Cersei dismisses the plan as impractical. Kevan is also indirectly (and inaccurately) accused of being a "half-wit with a stutter" by King Robert when he taunts Lancel about his alliterative name.
Kevan is going over troop movements with his brother Tywin in their army's command tent when Tyrion enters, having escaped from his capture by Catelyn Stark, and with a makeshift army of hill tribesmen in tow. Kevan is pleasantly surprised to see Tyrion safe and free, though Tyrion's own father seems mildly disappointed at both prospects. Kevan explains that Jaime crushed the Tully army at the Battle of the Golden Tooth and is laying siege to Riverrun. Tyrion wonders how King Robert would allow this, but Tywin explains that Robert is dead and Eddard Stark imprisoned. A messenger then arrives saying that Robb Stark's army has passed south of the Neck. Tywin orders Kevan to have the drummers signal the army to assemble to march, and to send word to Jaime that their army will be moving against Robb.
Kevan is later part of Tywin's pre-battle strategy meeting, in which Tywin declares that Tyrion and his hill tribe allies will be in the vanguard. Tyrion balks at this, not only because it will put him in the greatest danger, but because the hill tribes are inexperienced at pitched battle. Kevan tries to console his nephew that the hill tribes do seem to be rather ferocious, and should be up for it. Kevan takes part in the following Battle of the Green Fork, and Tywin's army is victorious. Even Tyrion and his hill tribes did fairly well. It turns out, however, that this was simply a diversionary force so Robb could use the bulk of his army to ambush the western half of the Lannister army under Jaime at Riverrun.
Following the Lannister defeat at the Battle of the Whispering Wood and the capture of Jaime, Kevan joins Tywin's council as they discuss their next move. Kevan points out that with the Starks attacking from the north and both of Robert Baratheon's brothers attacking in southern Westeros, they are facing a war on two fronts. With half of their armies destroyed, Kevan asks if they should consider negotiating with Robb Stark for peace. Tyrion bluntly points out that all chance for a negotiated peace died with Robb's father Eddard, whom Joffrey petulantly had executed. Tywin angrily orders everyone out, except for Tyrion. He agrees that they could have negotiated if Eddard was still alive, but now they cannot hold their position, so he and Kevan will lead their remaining army-group south to regroup at Harrenhal.
Ser Kevan is present at a war council held at Tywin's chambers at Harrenhal; he predicts that King’s Landing will fall an hour after King Stannis Baratheon's forces arrive. Kevan counsels Tywin to order Cersei and her family to flee to the safety of Casterly Rock. Tywin balks at surrendering the Iron Throne. Kevan argues that giving up the throne is better than seeing the heads of their relatives mounted on the city gates, fearing that Stannis will execute any Lannister he finds in the city. Tywin rejects the suggestion, believing that a king who runs cannot remain king for long.
Tywin complains that Stannis is just two days from King's Landing while Robb Stark is on their doorstep in the Westerlands. Kevan reports word from their scouts that Robb remains north of Ashemark. Tywin laughs derisively and says that the last time their scouts assured them of Robb's movements they were lured into a trap. Tywin blames their poor intelligence for the capture of Jaime. Tywin asserts that Robb has gotten too close to Casterly Rock. Kevan relays news that Robb has sent a splinter force to recapture Winterfell and theorizes that the Greyjoys' seizure of the castle is a boon to them because Robb will not march against Casterly Rock until he is at full strength. Tywin dismisses the suggestion and opts to march on the Westerlands, leaving the defense of the capital to his allies.
Kevan's youngest sons, Willem and Martyn Lannister, are taken hostage at the Battle of Stone Mill and held temporarily by House Tully in Riverrun. Soon after their capture, they are murdered by Lord Rickard Karstark, who plotted to avenge the death of his son Torrhen Karstark, who was murdered by Jaime Lannister.
Following his brother's death, Kevan is present at Tywin's wake alongside his son Lancel. He apologizes to Cersei for the appearance of his son, who has joined a religious group known as the Sparrows. Kevan believes that religion has its place, but he dismisses them as "bloody fanatics" and states that they never would have set foot in the capital while Tywin was alive.
Kevan sits on the Small Council when Cersei announces that she is taking over control of the body until the King chooses a new Hand of the King. After appointing Lord Mace Tyrell as the new Master of Coin, Qyburn as the new Master of Whisperers and dismissing Grand Maester Pycelle's and Mace Tyrell's request to be appointed acting Hand, Cersei offers Kevan the new position of Master of War, in his capacity as leader of the Lannister armies in the wake of Tywin's death. Kevan demands to hear the news of his appointment from King Tommen himself but Cersei says that she is speaking in his name for the time being and that he is learning what it means to be a ruler from Cersei.
Angered by her blatant seizure of power at her son's detriment and by her addition of sycophants such as Qyburn to the Small Council, Kevan refuses to recognize her authority and informs her that, in his eyes, she is the Queen Mother, nothing more. As he stands to leave, Cersei angrily berates him for abandoning the King in his time of need. Kevan tells her that, should the King ask for him, he would be waiting for him at Casterly Rock before leaving the Small Council chamber.
Following Cersei's arrest by the High Sparrow, Grand Maester Pycelle sends a raven to Casterly Rock to summon Kevan back to King's Landing to serve as the Hand of the King. Kevan now presides over the small council. When Cersei asks Qyburn to ask Kevan to come to see her in her cell, Qyburn says he already asked and Kevan refused.
Kevan is present alongside Pycelle when Cersei returns to the Red Keep after her walk of atonement. Kevan remains stern and silent as Qyburn fawns over Cersei, presumably having not yet forgiven her for disgracing his son Lancel.
Kevan remains as Hand of the King and presides over the Small Council, which is now composed of Grand Maester Pycelle and Mace and Olenna Tyrell, who insist that they handle the situation of Loras and Queen Margaery's imprisonment. As Pycelle voices complaints against Qyburn and his experimentation on Gregor Clegane, the monster in question arrives with Jaime and Cersei Lannister to everyone's surprise. Both Kevan and Olenna remind Cersei of her place, but Jamie asserts they can stay, since a Lord Commander of the Kingsguard has always held a position on the council. Cersei chastises her uncle for ignoring Myrcella's untimely death, while Jaime informs him they have much to discuss now that Ellaria and the Sand Snakes have seized control of Dorne. Instead, Kevan refuses to talk while Clegane is present and promptly leaves the council chamber, followed by Pycelle and the Tyrells.
Days later, while discussing the situation with Olenna Tyrell, Kevan is once again approached by Cersei and Jamie. This time, however, Jamie convinces his uncle to keep the Lannister army in reserve when the Tyrell forces arrive to free Margaery and Loras. Despite Cersei's promise to return Lancel, Kevan warns them the Sparrows have many supporters in the city, and many more could die in the coming civil war.
The plan fails when Tommen, Margaery and the High Sparrow shockingly reveal a holy alliance of the Crown and the Faith. In the throne room, Kevan stands at Tommen's right hand with a worried look when he strips Jaime of his position in the Kingsguard because "an attack on the Faith is an attack on the Crown", though he will continue to serve Tommen outside King's Landing.
Before a sudden royal announcement, Cersei asks why she was not informed of the event, and Kevan responds it was only recently announced. Cersei wishes to stand by her son, but Kevan instead orders her to stand with the other ladies at court, much to her dismay. Kevan witnesses Tommen announce the date for Cersei and Loras' trial and outlaw trial by combat throughout the Seven Kingdoms.
As the younger brother of the Lord Tywin Lannister, Kevan understood he couldn't compete with the powerful lord. After Tywin's death, Kevan opted to return to Casterly Rock rather than recognize Cersei's authority. He returned to King's Landing to become Hand of the King when Cersei was imprisoned, and wants to deny Cersei all autority and iunfluence. He was killed when the Sept of Baelor exploded.