In her first appearance in the series, Kat is a rookie Viper pilot aboard the Battlestar Galactica, part of a group being trained by then Lieutenant Kara Thrace (Starbuck). Although a rookie, she is very sharp and talented, and quickly becomes a hot-shot pilot, taking part in a vital operation to attack a Cylon tylium refinery base.
As the fatigue and stress of weeks of continuous duty without relief mount, Kat turns to stimulants to keep her senses sharp. Ultimately, she overdoses on stims, becomes hysterical, and finds herself unable to safely land her Viper. She is talked down into a near crash-landing by her former instructor, Starbuck, and is temporarily hospitalized.
After Captain Lee "Apollo" Adama and Starbuck are transferred to the Battlestar Pegasus by Admiral Helena Cain, Kat becomes Galactica's senior pilot, leading the Galactica Air Wing in what amounts to a game of "chicken" with the Pegasus Air Wing.
The rivalry between Kat and Starbuck, arguably the two best pilots on Galactica, intensifies with the passage of time. Kat comes to disdain her former flight instructor on account of her drunken and irresponsible behavior; Starbuck considers Kat to be an upstart with a too-high opinion of her own abilities. Circumstances lead to Starbuck and Kat flying as a pair on a Combat air patrol during which they encounter the ace Cylon Raider nicknamed "Scar." Starbuck is the first to spot "Scar," and comes close to trying to kill "him" in suicidal head-on pass; at the last moment, she breaks away and lures "Scar" into Kat's line of fire. As Kat is the one who fires the killing shots, she earns the title of Galactica's "Top Gun", thereby also winning a personal bet against Starbuck.
During the settlement of New Caprica, with Commander Lee Adama in command of Pegasus and Starbuck down on the ground, Kat becomes the CAG of Galactica, leading the decoy attacks that lured the Cylons away from New Caprica, clearing the way for Galactica to jump in and deploy the real strike force. Following the successful recovery of the civilian population from New Caprica and the destruction of the Pegasus, Lee Adama resumes his old post of CAG: however, Kat remains a senior member of Galactica's Air Wing as a squadron leader.
As the Galactica and its Raptors guide the civilian fleet in relays through a treacherous stellar cluster, it is revealed the real Louanne Katraine was a woman who died two days prior to the Cylon attack on Caprica. A drug runner by the name of Sasha, seeking to change her life, took the deceased's identity and became the individual known thereafter as Louanne "Kat" Katraine. After Starbuck discovers this, Kat begs her not to inform Admiral William Adama but instead to allow Kat to do so herself. On the fourth and penultimate relay through the cluster, Kat receives a dose of radiation sufficient to have her removed from flight status, and begins losing hair. She chooses to accept her past and present life: she has a sexual encounter with her former associate Enzo, swaps her radiation badge for that of Captain Karl "Helo" Agathon, and boards her Raptor for the last time. She stays in the cluster after Admiral Adama issues the jump order in order to see her assigned ship, the Faru Sadin, safely to the other side. In doing so, she receives a fatal dose of radiation. Admiral Adama visits her deathbed. He later promotes her posthumously to CAG on account of her bravery. Kat tries to tell Adama the truth about her past, but Adama, perhaps suspecting what she's going to reveal (in a deleted scene for Exodus Part 2 he indicated he already had some idea), tells her not to tell him, not caring about her past but about what she had done stating that what brought her to that point didn't matter. Although it was not made explicit in the scene, Battlestar Galactica showrunner Ronald D. Moore made it clear in his podcast for "The Passage" it was intended that Adama should look on Katraine, like Kara Thrace, as an "adopted daughter" of sorts.