Tarrlok was born in the Northern Water Tribe to the former crime boss, Yakone, and was the second and youngest son in his family. He and his older brother, Noatak, formed a strong brotherly bond between each other, until they both discovered they had the ability to waterbend. Soon after, Yakone revealed his past life (and how his bending had been severed by Avatar Aang) and introduced them to the art of bloodbending, a sadistic form of waterbending used to manipulate others by bending the blood within their bodies.
Yakone would take the boys on nightly "hunting" trips in order to keep their secret hidden from their mother, training them in the bloodbending method. Tarrlok showed restraint, harboring no desire to harm the helpless animals his father had them practice on, but his brother progressed in his newfound abilities, overriding Tarrlok and being favored by Yakone. Despite this, however, Noatak soon became detached, as Tarrlok describes, and became increasingly depressed.
Yakone eventually encouraged the brothers to bloodbend each other and, while Noatak showed no restraint, he later defended Tarrlok when he hesitated to do the same. Noatak declared that Yakone was weak (seeing as how his bending was removed), that bloodbending was not the most powerful form of bending, and flung him into the snow, urging Tarrlok to join him in his escape. Tarrlok refused however, concerned of the effect this would have on their mother, and Noatak who stated he was indeed a weakling escaped without him.
Tarrlok and Yakone spent several days searching the tundra, but they eventually came to the conclusion that Noatak had perished in the harsh snow and returned home without him, sending the family into a state of depression. Yakone passed away soon after and Tarrlok later moved to Republic City in order to start life anew, making his way into political power and presenting himself as a "savior" to the common people. He was then established as Councilman Tarrlok and became a representative for the Northern Water Tribe.
Shortly after Avatar Korra's arrival in Republic City, Tarrlok gets the council (except Tenzin) to unanimously agree with his plans to organize a special task force in order to put an end to the Equalist movement. Upon its approval, he then attempts to persuade Korra to join his task force. Korra refuses his offer, much to the surprise of Tenzin and Tarrlok. After several failed attempts involving bribery through lavish gifts, Tarrlok decides to hold a gala in her honor in City Hall, hiring several journalists to question her refusal to join the task force. Under pressure, Korra announces that she will finally agree to join the task force, despite her reluctance.
Tarrlok later orchestrates a nighttime raid on a secret Equalist training facility beneath a bookstore located in the Dragon Flats district of Republic City. With the help of Avatar Korra, Tarrlok and his task force manage to capture and arrest several Equalist members. At a conference meeting, Tarrlok announces the success of the raid and states that Republic City has nothing to fear with himself and the Avatar leading the charge. Korra then publicly challenges Amon to a duel on Avatar Aang Memorial Island via radio broadcast and by witness of city journalists.
Tarrlok encourages and organizes the duel later that night, stationing several authoritative zeppelins throughout the area, and assuring Tenzin that if anything goes wrong under circumstance, city officials will arrive accordingly to keep the Equalists at bay.
Later, when Amon theatended to shut down the pro-bending arena, Tarrlok, Tenzin, and the rest of the council agreed to shut down the arena and cancel the championship tournament, despite the Fire Ferrets' dismay. Chief Lin Beifong, however, disrupted the meeting and offered to provide the arena with extra security during the match, with Tarrlok, along with the council, agreeing to the proposal.
Following a successful Equalist attack on the arena, however, Tarrlok called a press conference, in which he boldly placed the blame on Chief Beifong, stating the police force needed new leadership in order to meet amends during the dire situation. The former chief's resignation allowed Tarrlok to increase his influence and power, through Saikhan's appoinment as the new chief. When Korra and Tenzin confronted Tarrlok after the conference, he offered Korra another opportunity to rejoin his task force, considering the conclusion of the pro-bending tournament, but when Korra refused his "vanity project", Tarrlok insulted her by stating she had not yet mastered airbending and ordered her to avoid interference with the law.
At the following council meeting, Tarrlok proposed a law establishing a curfew for all non-benders and the illegalizing of Equalist association. The law went into effect with relative ease as Tenzin was the only dissenting vote. Tarrlok then went as far as to cut off the power of local non-benders, which sparked a non-bender protest (many of which were ordinary citizens) in the Dragon Flats district. Tarrlok ordered the police to capture the citizens by rounding them up, until each of them were proven innocent. When Team Avatar confronted Tarrlok during the protest and argued against him.
Later that night, Korra confronted Tarrlok herself at his office in order to intimidate him into compliance to free her friends, along with the non-benders, from imprisonment. Tarrlok then offered to free her friends, as long as she obey his command, to Korra's refusal. When Korra stated he was just as bad as Amon, Tarrlok went into a rampage and began a duel. Korra managed to utilize her earthbending by releasing the wall behind Tarrlok and closing it in on him, leaving him without a source of water, pushing him down to the Council meeting room. As a last resort, Tarrlok bloodbent Korra into submission and captured her, recklessly driving her off in a police vehicle to the surrounding woodland of Republic City, holding her hostage in an old mountain lodge.
During the same night, he obtained an Equalist glove, shocked himself, and laid out "evidence" as to confirm an Equalist attack. When Tenzin, Lin, and, after having been freed, Korra's friends, investigated the matter by infiltrating an Equalist facility, they discovered that Tarrlok had abducted Korra, not the Equalists. When Tarrlok denied the act, his assistant, the council page, confirmed the incident and revealed Tarrlok's secret bloodbending abilities. Tarrlok, realising he was defeated, bloodbent everyone in order to make an easy escape. He then confronted Korra at the lodge, after she had discovered that he was Yakone's son, and blamed Korra for the devastation that had amassed.
Before leaving, he told Korra that he would start a new life elsewhere and take her as his hostage. As he was going up the stairs, however, he soon discovered that Amon and several Equalists were awaiting him. Tarrlok managed to successfully bloodbend and subdue everyone, except Amon, who then proceeds to remove Tarrlok's bending, paralyzing him for a period of time, then throwing him into the back of a truck.
Prior to his death, Korra and Mako found Tarrlok imprisoned in a separate cell during the Republic City battle, just moments before the Equalist Victory Rally. Tarrlok revealed his tragic past as Amon's brother and Korra and Mako proceeded to take down Amon, using the evidence obtained from Tarrlok to reveal Amon's true identity in the presence of his dedicated followers. Prior to their departure, Tarrlok gave the two a sincere apology over his actions and lamented on how he and his brother became no better than their father. He also turned down an offer by Korra to free him, believing this would alert Amon.
When Amon had fled the battle after having revealed his waterbending abilities and being overcome by both Korra and Mako, he freed Tarrlok and offered him to join him in an escape to begin life anew. The brothers used a speedboat across the Mo Ce Sea, during which Amon proclaimed, now reunited with Tarrlok, that there was nothing they couldn't accomplish together. At the mention of Amon's birth name, "Noatak", Amon began to reminisce on their brotherhood, shedding a single tear before Tarrlok utilized a nearby Equalist glove to ignite the fuel tank behind him, killing them both in the resulting explosion.
- The relationship between two brothers is similar of Lee Kang-To's relationship with his brother where Kang-san was masked hero and killed by his own brother unknowingly and become second Birdal Mask.
- His Polish voice actor also voiced Megamind and Chester V.