Little is known about T-Dog's life before the apocalypse. He lived in Georgia; it's unknown whether he was living specifically in Atlanta or if he was living elsewhere. According to Glenn, T-Dog was very religious and used a van from his church to help evacuate elderly residents to refugee centers before finding and rescuing Glenn.
T-Dog first appears in the episode "Guts" with a scouting party from the Atlanta camp consisting of Andrea, Glenn, Jacqui, Morales and Merle. Whilst in the city looking for supplies, the group take refuge on the rooftop of a department store and the hot-headed Merle starts firing on the zombie masses with a sniper rifle. T-Dog yells at Merle for wasting bullets and attracting more walkers, but the racist Merle responds by calling him a "nigger", causing T-Dog to take a swing at him. Dixon proceeded to beat T-Dog brutally, and spits on him. Before Merle could do any further harm, Rick handcuffed him to a pipe. Later, T-Dog was assigned to watch Merle as the other survivors attempted to find a way out of the building they were stranded in. Merle tried to sway T-Dog into handing him the hacksaw by saying that he and T-Dog can come to some sort of parley. When the survivors were getting ready to escape, T-Dog dropped the handcuff key down a hole by accident and was forced to leave Merle on the roof, but not before locking the rooftop door shut with a padlock. He then escapes from Atlanta with his fellow survivors after Glenn and Rick drive a truck to the department store loading dock.
T-Dog is truly apologetic regarding leaving Merle on the rooftop and assures everyone that it was indeed an accident. Unfortunately, T-Dog is unable to make amends as Merle is gone when he, Rick and Daryl go back for him. All that remains of Merle is a severed hand which Merle evidently cut off himself using a hacksaw. No body is found nearby so the group consider the possibility that Merle is still alive.
T-Dog remains with Rick and the majority of the group following the attack on the Atlanta camp and after their encounter with Dr. Jenner. While the group are looking for supplies in a cluster of abandoned cars on the highway, a massive herd of zombies passes through and the survivors try to hide. T-Dog accidentally cuts his arm on a broken car door, attracting a couple of zombies with the scent of fresh blood, but Daryl saves T-Dog's life by throwing a corpse on top of him, masking his scent.
After Sophia goes missing, Rick tells T-Dog and Dale to stay with the RV while the others go looking for her. During their time hanging around the RV, he begins to show signs of hallucination, believing that the other survivors are leaving him and Dale behind because Dale is old and he is black. After speaking to Dale about this, it is revealed that T-Dog has a major case of blood poisoning. Dale scavenges for antibiotics, but finds nothing until Daryl returns and shows him Merle's old stash of drugs.T-Dog's wound and infection are later treated after the group arrive at the Greene family farm.
During the group's encampment at the farm, T-Dog contributes by teaching Hershel's children to shoot and regularly taking watch. During the episode "Judge, Jury, Executioner", he joins the group's debate over what to do with the captive Randall, whether to let him go or to kill him so he cannot tell his own group about the farm. T-Dog votes for Randall's execution, but the final decision is put on hold following Dale's sudden death and the decision becomes moot after Shane later takes Randall out into the woods and murders him.
T-Dog is among those who survive the zombie attack on the farm and helps with clearing the walker infestation in the yard when the group reach the prison. He is among the group clearing out the zombies in the tunnels and is present when Rick amputates Hershel's leg after he is bitten. He is wounded by a zombie when the prisoner Andrew lures a horde of walkers into the prison in order to kill off Rick and his group.
In the third season episode "The Killer Within", T-Dog is bitten by a zombie when a swarm of them pour in through a gate that Andrew had opened. He decides to use his last hours of life helping Carol to get back to Cell Block C in safety, ignoring Carol as she tells him that he should rest because of the bite. They reach the corridor that leads to the laundry room, but it is blocked by two walkers. Carol insists that they should go back and find another way, but T-Dog heroically charges the two walkers against the wall and tells Carol to escape while she can. Carol runs to the laundry room, when she looks back, the two walkers are tearing into T-Dog's body. T-Dog, knowing he was doomed after the first bite, cries out to Carol to go while the zombies eat him alive.
Later, Rick goes down into the tunnels and finds T-Dog's remains still being eaten by the two walkers and shoots both of them. It appears that there was not enough left of T-Dog to reanimate.