Garlett played his early football for Burracoppin, before playing for Swan Districts in the West Australian Football League in 2007. Garlett was homeless for much of the time that he was playing for Swans, often sleeping in the back of cars going for days without eating. Once the club discovered this, he lived with Anne and Maurice Embley (parents of many Swan Districts players, including West Coast's Andrew Embley) and with Swans captain Shane Beros. Altogether, Garlett played 21 league matches for Swans between 2007 and 2008.
Garlett was made a nominated rookie in 2010, and earned regular selection in the Carlton team. He scored a career-high six goals in Round 19 against Essendon and was subsequently rewarded for this by taking out the NAB Rising Star nomination for the round; he ultimately polled five votes to finish sixth for the Rising Star Award. He played twenty games for the year, and performed strongly in the club's best and fairest, finishing seventh. Throughout the season, he formed part of a short-lived forward-line structure consisting of tall full-forward Setanta Ó hAilpín, and three small forwards (Garlett, Eddie Betts and Chris Yarran) who became known as "Setanta's Little Helpers".
Garlett signed a two-year contract extension with the Blues, and moved onto the senior list proper in 2011. He played every game in 2011, and kicked 50 goals for the year.