Gawn was recruited by the Melbourne Football Club with their fifth selection and thirty-fourth overall in the 2009 national draft. At the time of the draft, he was the second tallest player in the league at 208 cm, behind Aaron Sandilands at 211 cm. After undergoing surgery in 2009 to repair his ACL, he missed the majority of the 2010 season. He played a few matches at the end of the season for Melbourne's affiliate team, the Casey Scorpions, in the Victorian Football League (VFL) development league. After strong performances in the VFL for Casey in the first half of 2011, he made his AFL debut in the thirty-three point win against Essendon at the Melbourne Cricket Ground in round eleven, where he played primarily as a forward and recorded eight disposals, ten hitouts and two behinds. For his debut match, he had the number 37 jumper presented to him by 1991 Brownlow Medallist, Australian football and Melbourne hall of famer, Jim Stynes, who wore the same guernsey number in his first season. He played in the next two matches before being omitted for the round fourteen match. He returned to the senior side for the seventy-six point loss against Carlton at the Melbourne Cricket Ground in round 20, but he was dropped the next week and managed four matches in his debut season.