Thief: The Dark Project, the first title of the series, opens by describing a scene from Garrett's youth where the young thief is caught attempting to pick the pocket of a hooded man in a dark alley. The hooded man is impressed, for it is not easy to spot a Keeper who does not wish to be seen, and offers the youth a place in the Keepers organization. Garrett accepts but, after many years of training, leaves due to a "folly of anger" that is never fully described in the series. Without the Keepers' control, Garrett decides to put his skills to more "personal" use and becomes a contract thief.
Throughout the series Garrett uses an array of items and weapons that include a sword (or a dagger in Thief: Deadly Shadows) , a blackjack, and several types of many-faceted arrows. Starting at the end of The Dark Project, Garrett also has one of his eyes replaced with a mechanical one that gives him the ability to zoom his vision and see in the dark.
Some of his arrows include
- Gas arrow - Knocks most enemies unconscious.
- Fire Arrow - Lights torches and kills enemies.
- Water Arrow - Puts out torches and cleans up blood.
Some of the items and weapons that Garrett can use change throughout the series. He sometimes has access to proximity mines, gas grenades, and in the earlier games, vine arrows that create a rope for Garrett to climb. Thief: Deadly Shadows removed these arrows and gave Garrett the ability to climb certain walls with climbing gloves.
Garrett uses his mastery of stealth and array of items to achieve his goals. "Moss Arrows" can cover loud surfaces with spots of moss so that walking makes no noise. The "Blackjack" can be used to silently incapacitate enemies so that their bodies can be moved and hidden. "Noise Arrows" (and as of Thief: Deadly Shadows, any physics enabled objects) can be used to create a distraction that can move guards away from inconvenient posts.
Each title of the Thief series also provides Garrett with several different factions that he either aids or battles. Most notable of these are: the vengeful City Watch, the shadowy Keepers, the fanatic Order of the Hammer (or Hammerites), and the mystical Pagans.
Garret is known for his sardonic, apathetic commentary from the shadows.
- "Good thing you're dying, Cutty. Or I'd have to kill you for stiffing me. AGAIN."
- "Fanatics make unreliable friends."
- "It's a rock. It's what you asked for. Am I gonna get paid or not?"
- "Bafford, like most of his kind, probably keeps his treasures on the top floor of the place. Close to his heart...and far from his servants."
- "Heh! It's a throne room. How pretentious can you get?"
- "I went to Cutty's place to deliver the scepter, but Cutty wasn't there. He'd been arrested by the Hammerites. Apparently they didn't approve of his occupation, and I doubt they approve of mine. So hopefully they'll never catch sight of me when I break him out of their prison. Which is what I'm going to do."
- "I'd rather not have to do this job, but Cutty's a reliable fence, and I don't appreciate the Hammerites abducting him. And he owes me money for the Bafford job..."
- "I was pissed at Cutty for a good while after the...prison debacle. But hey, you can't blame him for what the Hammers did to him. So I decided to go after that horn Felix talked about. Not like I had a whole lot of choice, really...the rent is due...and my landlord's even tougher than the Hammers."
- "Felix, always helpful, also said that the catacombs are supposed to be haunted. Think I'll go make some inquiries about where a 'heretic' like me can get some holy water. Always go prepared..."
- "Tombs with piped in music. How classy."
- "Apparently their leaders...Donal and Reuben...are arguing over the prized sapphire vase. Sounds like they could use a third party to settle their disagreement. Since I'm no mediator, I'll just steal the vase from them. They'll be so busy blaming each other no one will suspect an outsider."
- "I guess if you're rich enough you can build any sort of madhouse to live in."
- "Those crazy Hammers. You know, it wouldn't hurt to have a dozen of heavily armed fanatics by my side. I'll drop by their temple and explain things, hopefully they'll be so distracted with the Trickster's return that they'll forget to hold a grudge. And even if they don't, I know how to get out of Cragscleft prison already."
- "If you hadn't noticed, I just saved the world. Yourself included."
- "I've always equated feelings with getting caught; they both get in the way of my money."
- "Huh! Wasn't that long ago that I was planning on my retirement...now the only thing that's getting retired is my standards."
- "Looks like I have something useful to learn from a seminary for a change."
- "If I believed in it, now it would be a good time for me to wish for luck."
- "Huh! This proves it...going legit is more trouble than it's worth..."
- "I'm not surprised that the Mechanists are not the saints they claim to be, no one in this city is."
- "Judging by the look on Sunny's face, I'd say he sold me out."
- "Iron trees? Not in my part of town."
- "I know they're trying to manipulate me, but keepers never alter the truth... just keep it in the shadows."
- "I'd rather not tread where the dead sleep."
- "Angelwatch? Is this how our arrangement is gonna work, you coming up with ways for me to get myself killed?"
- "So this is the city of the future? I prefer my Tenement instead."
- "What is locked - can be opened. What is hidden - can be found. What is yours - can be mine."
- "A secret room... always my favourite room in a house."
- "Let me see if I've got this right. You want me to find Gamall's lair, learn what she wants your treasure for, and find and destroy this final glyph? Anything else?"
- "It's not much. But it's home" (upon entering his house).