Garrett studied video production at university and initially intended to be a games journalist. His early YouTube work consisted of "Let's Play" videos which he made for his own amusement. When he noticed that his primary audience was children, he reoriented his work to be family-friendly. When the videos became popular, Garrett left his job as a barman to focus on producing the content full-time.
Garrett's YouTube channel is aimed at children, and his audience is largely 6 to 14-year-olds. As the character of Stampy Cat, an orange and white cat, Garrett tells stories within Minecraft and other games. He gives viewers ideas for activities to pursue with their friends. Garrett describes the character as "a bigger, brighter, better version" of himself. He receives correspondence from his viewers and thinks they see him as a friend, rather than "a presenter in a studio".Other characters in the videos include iBallisticSquid, the YouTube name of Garrett's friend David Spencer, and Sqaishey Quack, a duck character played by Garrett's partner Bethany Bates. Jordan Shapiro of Forbes.com said that "he does a great job of bringing the positive aspects of Minecraft—the game’s educational potential—to the surface." Caroline Knorr of Common Sense Media describes Stampy's presentation as best for younger fans and that "Stampy feels a cross between Pee-Wee Herman and Mr. Rogers."
On 25 April 2015, Garrett launched a spinoff educational YouTube channel in collaboration with Maker Studios. The series, Wonder Quest, is scripted, professionally produced, and designed so that it can be used in classrooms. Garrett has also been attached to a Minecraft film. In July, he appeared on the series premiere of the Disney XD sitcom Gamer's Guide to Pretty Much Everythingwhere he portrays the announcer Stampy Cat at the World Gaming Championships. He was a featured panelist at MineCon held in London in July.
Garrett has signed a two-book deal with Egmont Publishing. Stampy's Lovely Bookwas released on 22 October 2015; aimed at ages 4 to 10, it features games, activities, jokes and facts about Stampy Cat and some of his Vlogger friends. Stampy Cat: Stick with Stampy! was released on 28 July 2016; the 32 paged paperback features sticker-based activities, games, jokes and posters.