|“||You’ve just been ‘Garth-ed.’||”|
Garth is a hunter who generally works alone, although he has teamed up with the Winchesters on three separate occasions and once with Bobby, on a Rugaru hunt ( he almost got killed because he isn't that great of a hunter ). Garth drives a Ford Ranchero with shovels in the back, in case he needs to dig up a grave on a hunt. Once he puts a spirit to rest, he says that the spirit has been "Garthed." When he drives, he sometimes plays the song Poison by Bell Biv DeVoe.
After stepping up to fill Bobby's role, Garth becomes more serious and confident, as well as more capable at his job. He also adopts several of Bobby's mannerisms. He's described by Dean as someone who "grows on you."
Garth likes sweet things and comics, gets drunk easily, and appreciates a hot bath after a hard day's hunting. He likes giving hugs. Some time after Sam and Dean first meet him, Garth began a relationship with a "special lady" who knows about his hunting and also has twins.
Garth calls Bobby for some help on a case he's working, and Bobby tells him that it doesn't sound like a Vampire. He advises him to call the FBI with a tip, so Garth hangs up and calls the FBI... Agent Willis, that is. When Bobby realizes that Garth has called him instead of the actual FBI, he is exasperated. We only hear Bobby's side of the conversation.
- Bobby: Yeah, Garth, what do you got? ... Never heard of a vamp doin that. It doesn't sound like our kind of thing. Better drop a dime to the FBI.
- Bobby hangs up the phone. Another phone labeled FBI Tom Willis rings.
- Bobby: Willis, FBI. ... No, Garth, not me the FBI. The real FBI! How are you still alive?
Bobby sends Garth to Pike Creek, Delaware to help Dean work on a case, as Sam is under a spell by Becky Rosen. Dean shows him a newspaper article about people who have had good things happen to them recently and are now mysteriously dying in freak accidents. Posing as press, they head to an insurance company where a man was just promoted from junior salesman to CEO, thinking he might be the next victim in their case. When Dean and Garth arrive at the insurance company, Sam and Becky are already leaving. Sam tells Dean that the new CEO, Craig, is clean but Dean and Garth still question him.
Dean and Garth become sure that the man's wife is the one behind his sudden success, so they confront her, but she refuses to admit to anything, that is, until they save her from being killed by a falling chandelier. Afterwards, she admits to making a deal with a demon. Garth tells her that she needs to get out of town for a few days while he and Dean figure things out. They break into Becky's apartment, and Garth sees Becky's last tweet on her laptop: 'Going on romantic trip with hubster!!!'. Later, after Sam convinces Becky to help them trap Guy, the crossroads demon behind all of the recent deaths, Garth uses blueberry vodka to draw a devil's trap which Becky then lights on fire to trap the demon. He and the other hunters then get attacked by Guy's accomplice, a demon named Jackson, but Becky manages to kill him with Ruby's knife. Crowley appears and takes Guy away to punish him for breaking deals. Back at Becky's apartment, Sam and Becky sign the annulment papers necessary to dissolve their marriage while Dean and Garth watch. Dean tells Garth that he "doesn't suck," and Garth gives him an uncomfortable hug before leaving in his car.
The ghost of Jenny Greentree is originally suspected to be behind the death of Trevor McAnn in Junction City, Kansas and Garth salts and burns her corpse. However, when the boy's brother Ray dies, Garth calls Dean and Sam for help in finding the real culprit. They learn it is a spirit known as a Shojo. Garth, with help from Mr Fizzles, eventually figures out who the shojo's next victim is and tries to save him. Dean, with some help from Bobby's ghost, kills the shojo. As they part ways again, Garth hugs Dean for the 2nd time and even gives Sam a hug too, before driving off, but not before he remarks that he likes their car, an AMC Pacer.
Garth appears in Southern Comfort working on a case, and he reveals that he has taken over Bobby's role in the last year.
After hearing about Mary Lew crushing her husband's head with his own car, Garth heads to Kearny, Missouri where he poses as, of all things, a Texas Ranger—he claims that wearing a suit makes him look like a funeral director.
Garth has taken Bobby's place among the hunting community as Sam and Dean disappeared for a year and someone needed to. Garth has taken to carrying multiple cell phones to presumably act as cover for other hunters like Bobby did, gives out information that hunters need, wears one of Bobby's hats and uses some of his old catchphrases though not correctly usually. Garth is excited to see Sam and Dean and hugs them, though Dean is not amused that he is "the new Bobby" and the way that he acts like him.
Together they investigate the case, discovering that Kate wrote the name Allcot on the wall in blood and that there is green goo. That night at a bar, Garth asks Dean where he was and Dean tells him Purgatory but brushes off questions of how he got out. Garth also reveals he was a dentist before becoming a hunter, and that was how he found his first case. Investigating the name, they discover it is an old girlfriend of the dead husband, but before they can go interrogate her, her son Scott killed someone and wrote the name Sussex on the wall in his blood leaving behind green goo as well. Dean and Garth interrogate the ex-girlfriend, deciding that she wasn't having an affair with the husband and that the wife is apparently holding a grudge for her husband hooking up with his ex on prom night. While Sam investigates, Garth and Dean go through Bobby's Journal for information on what they might be dealing with with Garth pointing out the noticeable tension between Sam and Dean and explaining why he has taken over Bobby's role, saying that Bobby belonged to everyone, not just Sam and Dean and is visibly upset while talking about Bobby.
Garth finds in Bobby's Journal that a ghost that leaves behind green goo is a Specter and that it is apparently woken up when its grave is disturbed. Garth finds out that the grave of the Confederate version of The Unknown Soldier has been disturbed, though apparently nothing was taken and that night, he, Sam and Dean go to salt and burn the soldier's bones, figuring that that should put the ghost to rest as it does with all other ghosts. Garth suggests they say something before burning the bones, but Dean just says "we win" before setting them on fire.
However, a deputy kills his boss and after finding more green goo at the scene, they realize the ghost isn't gone. After learning that the next person possessed headed for the hospital, Dean goes there to stop them while Sam and Garth go to the library to try to find out who the Unknown Soldier is. They learn a theory that it is Vance Collins, a Confederate soldier who was killed by his Union soldier brother. They realize that Vance had an Indian Head Penny that was stolen.
Sam and Garth rush off to let Dean know after he doesn't answer his phone, only to find him possessed by Vance and waiting to kill Sam. Garth tries to defuse the situation, believing that Dean won't kill him as he is not angry at him. When that fails, Garth punches Dean, causing him to drop the penny which Garth picks up, but is unaffected by Vance.
Garth is able to melt down the penny, putting Vance to rest though he tells Dean he had a hard time doing it. Garth explains to Dean that he has learned to let all of his grudges go and was thus unaffected by the spirit and Dean puts Bobby's hat back on his head, finally accepting Garth's new role. Garth drives off, giving advice to another hunter to run after learning he is being chased by a Wendigo without a flare gun or flamethrower to kill it with.
In Hunteri Heroici, it's revealed he has a safeboat, and is keeping Kevin and Linda Tran there for safety.
In LARP and the Real Girl, Garth called Sam and Dean to give them a case where a man had all of his limbs ripped off with no explanation. Garth has been tracking hunters via the GPS in their cell phones and now calls them with cases in the area they are in. Sam is visibly disturbed by this and tells Garth off for telling him "you've been Garthed" after explaining what he did. As a result, Sam tells Dean they need to disable the GPS in their phones so Garth can't do it again, though Dean admits that Bobby would have done the same.
In As Time Goes By, Henry Winchester has gone missing and Dean figures that he went to find the last two ingredients for a spell to return to 1958, Dean calls Garth to see if there are any hoodoo shops in the area. Apparently Garth gives him the info he needs as he is able to find Henry.
In Everybody Hates Hitler, Dean called Garth for information on the Thule Society, but neither Garth nor any of his contacts had even heard of it.
In Trial and Error, Kevin Tran mentions Garth as his only companion, that too only whenever he drops by.
He is also mentioned in Freaks and Geeks by Dean when he says that he'll be sending Garth to check on Krissy and the others from time to time and also by Victor Rogers who tells Sam and Dean that Garth must've been dropped on his head when he was a baby.
By Pac-Man Fever he is out searching for the missing Kevin, along with several other hunters.
After being missing for several months, Garth returns in Sharp Teeth where he is hit by a car after eviscerating a cow. Sam and Dean find him in the hospital, but he flees. When they follow him, Garth reveals that he is now a werewolf, having been bitten six months before on a hunt. Before he could kill himself, a werewolf named Bess Myers found him and he fell in love with her and married her. Ashamed of what he'd become, Garth disappeared so no one would know. Garth insists to Sam and Dean that his pack feed only on animal hearts and don't harm humans, coexisting with them and invites them to join their church services. Garth becomes frustrated with Dean when he remains hostile to Garth's new family and Dean explains what happened to Kevin Tran, saddening Garth greatly as he cared for the young Prophet. Soon afterwards, Garth and Bess disappear and Sam is kidnapped. The pack leader's wife, Joy and two other werewolves, Russ and Jobah reveal themselves to be plotting to bring about Ragnarok and rule over mankind and are going to murder Garth and Bess and frame Sam and Dean to galvanize the pack into joining them instead of their peace-loving ways. Garth pleads unsuccessfully for Bess' life, but Dean figures out the truth and comes to their rescue, killing the three rogue werewolves. In the aftermath, Garth offers to become a hunter again, using his werewolf powers to help, but Dean recognizes that the entire pack wasn't bad and that Garth has found happiness and tells him to stay with Bess and the werewolves. Garth also feels responsible for Kevin's death as he wasn't there, but Dean assures him it wasn't his fault and, much to Garth's pleased surprise, invites Garth to hug him before he changes his mind.
- Garth has been shown to have a very low tolerance for alcohol, becoming intoxicated after drinking a single beer.
- Garth once disguised himself as a member of the US Marines to gain access to a morgue in order to find out information on a case and on another occasion a Texas Ranger despite being in Missouri. He explained this as wearing a suit makes him look like a funeral director.
- He went to college and dental college and worked as a dentist for a while.
- Garth's first kill was the Tooth Fairy.
- Garth is evidently completely immune to Specters. As demonstrated in Southern Comfort, Garth simply says this is because he "[doesn't] hold grudges."
- Garth was initially supposed to be one of the hunters killed offscreen during the Leviathan outbreak. He was saved and included into the show by then show runner, Sera Gamble. 
- Garth is the third hunter shown to be turned into a monster: Gordon Walker was turned into a vampire as was Dean briefly before being cured. Garth has been turned into a werewolf, but poses no danger, so Sam and Dean leave him alone.
- Garth is able to play the piano very well.